On its face, the high-level meeting between U.S. and Russian officials held in Saudi Arabia, the first of its kind since the war in Ukraine began almost three years ago, was about kicking the Trump administration's push to end that conflict into hyperdrive.

But analysts as well as current and former senior officials told ABC News that more than the fate of Ukraine could hang in the balance, and the effects of the engagement are likely to have a significant impact across many of the nation's most significant relationships.

When Secretary of State Marco Rubio, national security adviser Mike Waltz and Steve Witkoff, President Donald Trump's special envoy to the Middle East-turned-go-to negotiator, emerged from their nearly five-hour session on Tuesday with Moscow representatives, they were all smiles.

"It was positive, upbeat, constructive," Witkoff said of the conversation. "We couldn't have imagined a better result after this, after this session. It was very, very solid."

Rubio also announced a tangible step to demonstrate the warming relationship between the United States and Russia -- announcing that both countries had agreed to staff up their respective missions in Washington and Moscow after a decade of tit-for-tat diplomatic expulsions had left the embassies running on skeleton crews.

"For us to be able to continue to move down this road, we need to have diplomatic facilities that are operating and functioning normally," he asserted.

Russia appeared to be in lockstep with the American delegation, as officials praised the meeting and spoke of improved prospects for thawing tensions between the countries.

"In order to prevent an improvement of Russia-U.S. relations from being torpedoed, we need to mend them, which is what we were doing today and, to be frank, not without success," Russian Foreign Minister Sergey Lavrov said.

In the wake of the meeting, it was clear that in the span of just a few hours, the dynamic between Russia and the U.S. had shifted more than it had during the last three years.

"Frankly, it's a clear signal that the former U.S. policy of trying to isolate Russia is over," said Bradley Bowman, the senior director of the Center on Military and Political Power at the Foundation for Defense of Democracies and a former national security adviser to members of the Senate. "We're in a new era now."

But for many, what was far from certain was whether these changes would benefit anyone besides the Kremlin.

Bowman pointed to Rubio's comment saying the U.S. and Russia had agreed to explore "both the geopolitical and economic cooperation that could result from an end to the conflict in Ukraine" after their conversation in Riyadh.

"I would call that a carrot, not a stick. So I get that that's trying to woo Putin in to say, 'Hey, look at all these things that you value you could have if you make peace.' That makes sense -- if you also have a stick element in there," Bowman said -- an element he argued the Trump administration's approach to Russia has so far lacked.

"I'm with President Trump. I want the human suffering to end," he continued. "But I also know from history and from a study of Putin and his KGB background that he tends to view concessions as green light for additional aggression, and if we don't negotiate from a position of strength, it's going to be a bad agreement or it won't be complied with for long by the Kremlin."

After the meeting in Saudi Arabia wrapped, Trump dialed up his team, according to the White House.

"This was a first step of many steps toward peace with the Russia-Ukraine conflict. It's a really significant milestone," White House press secretary Karoline Leavitt said on Tuesday. "The president remains committed to seeing this solved."

But even though Trump and Russian President Vladimir Putin were more than 5,000 miles apart when the meeting between the delegations was happening, laying the groundwork for their expected face-to-face meeting was high on the agenda.

After his call with Putin last week, Trump himself said the two would meet in Saudi Arabia as well, adding that it could happen "very soon."

When Waltz, his national security adviser, emerged from Tuesday's meeting, he said the delegations had not set a date but reiterated expectations that it would happen soon.

Behind the scenes in Washington, officials are bracing for the summit to come together at the same breakneck speed at which the dynamic between Russia and the U.S. had changed over the course of the last several days. One official told ABC News that the delegation had heard everything it needed to from the Russian delegation in order to move ahead confidently with the planning.

As part of the preparation, the White House is likely to strategize on what it hopes to achieve, particularly when it comes to concessions from Moscow -- because although the Trump administration's seemingly haphazard approach to ending the conflict has befuddled allies, the president is unlikely to relish the appearance of being outmaneuvered by Putin.

While Trump and his Cabinet have shown little interest in concessions Ukraine may have to make, the president has pointed to one thing he'd like to see Russia surrender: nuclear weapons.

The president told reporters gathered in the Oval Office on Thursday that he planned to fold Beijing into the conversation eventually as well and that he aimed to restart de-nuclearization talks with China and Russia and convince both nations to slash defense spending.

"There's no reason for us to be building brand-new nuclear weapons. We already have so many," he said. "We're all spending a lot of money that we could be spending on other things that are actually, hopefully, much more productive."

By conducting the Riyadh meeting bilaterally, Washington bypassed the powers on whose continent the war is playing out -- and left Ukraine, the victim of the war, out of the room.

Ukrainian President Volodymyr Zelenskyy said prior to the Riyadh meeting that Ukraine cannot "recognize" any agreement made without its participation.

Experts who spoke with ABC News said that whether a product of the U.S. strategy or not, Europe is beginning to discuss efforts to improve its defense capabilities seriously.

A Western official told ABC News that Washington sent a questionnaire to European capitals asking about the capabilities each country could provide for Kyiv as part of a security guarantee for Ukraine.

The questionnaire arriving in Europe was first reported by Reuters on Saturday.

French President Emmanuel Macron convened an emergency meeting of primary European powers on Monday, a side-by-side frame with the U.S.-Russia talks in the Middle East.

Ian Brzezinski, a senior fellow at the Atlantic Council and a former deputy assistant secretary of defense for Europe and NATO policy, said the U.S.-Russia meeting was an opening to discussions that was "not optimally configured," given the Europeans and Ukrainians were not in the first meeting on the Ukraine war.

"That's not just mystifying," he said. "It's troubling to the Europeans because it leaves them in the position where they could easily conclude that their future is being determined without them, and that's not a great way to develop confidence and trust and commitment."

Macron's presentation of a peacekeeping force in Ukraine, with early buy-in from the United Kingdom and Sweden, could shape into the diplomatic "stick" that Brzezinski said would rectify an insufficient defense commitment from Europe.

"What we do have is now a serious discussion by the Europeans to do something that they have failed to do over the last three years, which is to be willing to consider some sort of military presence in Ukraine," Brzezinski said. "And to me, that is a significant development and one that probably is of concern to Putin, particularly if it evolves in a way that leads to an American dimension in that force."

If Trump is able to motivate the Europeans to "do what they should have been doing a long time ago ... [by] carrying their share of the burden," the president could realize a victory that would appeal to him, he said.

U.S. Defense Secretary Pete Hegseth said at a meeting of the Ukraine Contact Group last week that credible security guarantees for Ukraine, which Zelenskyy said are indispensable to a truce, would need to "be backed by capable European and non-European troops."

"There will not be U.S. [troops] deployed to Ukraine," he added.

Brzezinski said a security guarantee should come in the form of a "deterrent force" instead of a peacekeeping force.

He said the questionnaire dispatched from Washington "may be an indication the administration is beginning to think seriously about a deterrent force."

"That would be good," he noted, "but for the deterrent force to be credible there has to be a U.S. dimension to it" -- meaning a U.S. force level of some 10% to 15% and air and missile defense.

George Beebe, the director of grand strategy at the Quincy Institute and a former director of the CIA's Russia analysis, said a European force in Ukraine would be unacceptable to Russia -- amounting to a "non-starter."

The two experts consulted by ABC News also differed over the sequence of negotiations.

The U.S. had "ample time" to meet with Ukraine and Europe before Russia, Brzezinski said, calling an initiation of talks with Russia alone a "mistake."

That a U.S. delegation met first with representatives from Moscow over the war in Ukraine was not significant, argued Beebe.

"I think the Trump administration recognizes that this war has multiple dimensions, one of which is bilateral, between Ukraine and Russia, and that requires direct Ukrainian participation in negotiations," he said. "But part of this is a bigger geopolitical context that largely is between Washington and Moscow."

He added that the administration likely doesn't intend to negotiate on Ukraine's behalf over the "disposition of territory," or the setting of potential new borders.

"I don't think that the Trump administration at all intends to cut the Ukrainians out," he said, adding that the disposition of territory "is not appropriate for the United States to do bilaterally with the Russians."

The meeting in Riyadh on Tuesday marked "a significant paradigm shift," according to Beebe, that reverses course from the Biden administration strategy, in tandem with Europe, to forgo diplomacy, leverage economic power and arm Ukraine.

"I think the major parts of that shift really are in the diagnosis of what caused this war," he said.

Part of the theory of the administration's case, Beebe said, is that the war is not "exclusively a case of Putin making an imperialistic land grab against his neighbor." Russia's invasion, by this diagnosis, was a response to the enlargement of NATO over the years.

Trump said Friday that the possibility of Ukraine joining NATO was "the reason the war started."

"Long before President Putin, Russia was very strong on the fact" that Ukraine should not join NATO, Trump said in the Oval Office.

"I believe that's the reason the war started," he said. "Because Biden went out and said they could join NATO."

He repeated the suggestion Ukraine was responsible for Russia's invasion, saying Kyiv "started it" and dismissing concerns that the country lacked a representative at the negotiating table in Saudi Arabia.

"You should have never started it. You could have made a deal," the president said, adding that he could've made a favorable deal.