Large parts of the Republican Party now treat Vladimir Putin as if he were an ideological ally. Putin, by contrast, continues to treat the U.S. as an enemy.

This combination is clearly unusual and sometimes confusing. It does not appear to stem from any compromising information that Putin has about Donald Trump, despite years of such claims from Democrats. Instead, Trump and many other Republicans seem to feel ideological sympathies with Putin’s version of right-wing authoritarian nationalism. They see the world dividing between a liberal left and an illiberal right, with both themselves and Putin — along with Viktor Orban of Hungary and some other world leaders — in the second category.

Whatever the explanation, the situation threatens decades of bipartisan consensus about U.S. national security.

Already, House Republicans have blocked further aid to Ukraine — a democracy and U.S. ally that Putin invaded. Without the aid, military experts say Russia will probably be able to take over more of Ukraine than it now holds.

If Trump wins a second term, he may go further. He has suggested that he might abandon the U.S. commitment to NATO, an alliance that exists to contain Russia and that Putin loathes. He recently invited Russia to “to do whatever the hell they want” to NATO countries that don’t spend enough on their own defense. (Near the end of his first term, he tried to pull American troops out of Germany, but President Biden rescinded the decision.)

Trump has also avoided criticizing Putin for the mysterious death this month of his most prominent domestic critic, Aleksei Navalny, and has repeatedly praised Putin as a strong and smart leader. In a town hall last year, Trump refused to say whether he wanted Ukraine or Russia to win the war.