It was a sharp shift change that signalled one thing: Joe Biden has had enough.

Still reeling from the killing of seven aid workers in Gaza by Israeli strikes, the US president told Benjamin Netanyahu there will be consequences if he does not start protecting civilians.

During a tense 30-minute phone call, a frustrated Mr Biden told the Israeli leader he needs to to take “immediate action” to implement a “series of specific, concrete, and measurable steps” to stop harming innocent lives.

US policy, he said, “will be determined” by how Israel acts.

If Mr Netanyahu refuses to heed Mr Biden’s warning and change his tactics, the world will be watching to see how America responds.

As Ben Rhodes, a former deputy national security adviser to Mr Obama has warned: “Bibi obviously doesn’t care what the US says, its about what the US does.”

So what tools does Mr Biden have when it comes to getting a bullish leader like Mr Netanyahu to act?

Halting or restricting arms sales

The White House stopped short of directly saying Mr Biden would halt arms supplies to Israel or impose conditions on their use, but this is the most obvious - and likely most effective - weapon in Mr Biden’s arsenal.

Despite pleas from some corners of his own party, the Democrat leader has long resisted curbing the flow of artillery and weapons to Israel, which is reliant on everything from US-made F-35 aircrafts to precision-guided bombs and artillery shells.

“When they say there’ll be consequences, I think this is kind of the most, this is the most critical one,” said Dan Arbell, a scholar-in-residence at the Center for Israeli Studies at American University.

“They haven’t reached it [yet], but I wouldn’t rule it out in the near future if the situation continues as it does,” he told The Telegraph.

Steven A Cook, the Eni Enrico Mattei senior fellow for Middle East and Africa studies at the Council of Foreign Relations, said “there really (was) no other point of leverage for the United States” other than restricting military aid.

“Now that he [Biden] has essentially threatened action, he would be weak not to follow through if the Israelis do not perform,” he said.

Subtle but powerful messaging

Rather than making overt, public moves to cut off arms deals, Mr Biden could also make subtle changes to hold-up contracts and frustrate Tel Aviv.

“Sometimes the strongest signals are actually very quiet ones,” said Natan Sachs, the director of the Center for Middle East Policy at Washington-based non-profit the Brookings Institution.

This could include snowballing the provision of munitions or the approval of mundane contracts for spare parts.

“At the working level that’s often where you see the most powerful messaging and it’s one the security establishment the government take very seriously,” he told The Telegraph.

While it might seem incremental, this would be a “ratcheting up by the Americans” and something the Israelis would “take to heart”.

Ramp up public attacks

Mr Biden and his cabinet’s remarks on Mr Netanyahu have become increasingly spikey in recent weeks.

The US president called this week’s killing of seven World Central Kitchen aid workers “outrageous” while Secretary of State Antony Blinken condemned the “horrific attack”.

Meanwhile, Senate majority leader Chuck Schumer last month branded Mr Netanyahu an obstacle to peace and called for elections in Israel.

Mr Abell expects critical statements and damning terminology to be used more frequently in the coming weeks.

However, he adds, this tactic only has so much mileage as people quickly get used to verbal attacks.

Stop protecting Israel

The US has been a staunch supporter and protector of Israel.

In February it vetoed its third UN Security Council resolution demanding a ceasefire in Gaza.

When the US did not veto a resolution calling for an immediate ceasefire in the Gaza Strip last month, Mr Netanyahu retaliated by cancelling a Washington meeting between his delegation and the Biden administration.

Continuing to abstain from future votes is potentially a valuable tool for Mr Biden.

If the Democrat leader shows waning US support for Israel, it could also influence other countries’ treatment of the Jewish state.

Some nations, for example, may stop short of condemning Israel for fear of upsetting its American allies.

“If countries have less of a sense… that ‘America has Israel’s back, we better play nice’” it could make things harder for Mr Netanyahu, Mr Sachs adds.

Palestinian statehood

Palestinian statehood recognition, which is highly sensitive both internationally and domestically, is one of the least likely options Mr Biden could take.

While White House officials have said they are exploring policy options with regards to recognising a Palestinian state, such a move would have huge consequences.

Mr Abell warned such drastic action could end up playing into Mr Netanyahu’s hands.

“He’s at the lowest point in terms of Israeli public opinion and such a public confrontation could help him,” he said.

The Israeli leader will be able to say “it’s us against the world”, he added.

While you can’t rule it out, acknowledging a Palestinian state would be a major move with legal ramifications.

Such a drastic action is more likely to be carried out in “very calculated way” rather than as simply “a means of ratcheting up pressure”, Mr Sachs said.

“I don’t know which way they’ll go,” he told The Telegraph.

“I think the anger towards Netanyahu, the exasperation towards Netanyahu is very genuine... It’s brought even Biden to this moment.”