President Obama on Tuesday said that Donald Trump’s “flattery” of Russian President Vladimir Putin is “unprecedented,” and he called out Republicans who criticized the administration’s approach to Russia and then turned around and endorse Trump’s position on Putin.

“Mr. Trump’s continued flattery of Mr. Putin and the degree to which he appears to model many of his policies and approaches to politics on Mr. Putin is unprecedented in American politics. And is out of step with not just what Democrats think, but out of step with what, up until the last few months, almost every Republican thought, including some of the ones who are now endorsing Mr. Trump,” Obama said when asked about Trump’s comments about Putin during a press conference with the Italian prime minister.

Obama laid out his administration’s approach to Russia and noted that he has tried to work with Russia and Putin on “common international challenges.”

The President said that in Syria, “rather than to work with us to try to solve the problem, [Putin] doubled down on his support for Assad, and we know the situation that exists there.”

“So any characterization that somehow we have improperly challenged Russian aggression or have somehow tried to encroach on their legitimate interests is just wrong,” Obama said.

He told reporters that he does not understand how “some of the same leaders of the Republican Party who were constantly haranguing us for even talking to the Russians and who consistently took the most hawkish approaches to Russia, including Mr. Trump’s selection for vice president, now reconcile their endorsement of Mr. Trump with their previous views.”

“The bottom line is, is that we think that Russia is a large, important country with a military that is second only to ours, and has to be a part of the solution on the world stage rather than part of the problem,” Obama said. “But their behavior has undermined international norms and international rules in ways that we have to call them out on, and anybody who occupies this office should feel the same way, because these are values that we fought for and we protected.”

Obama said that he’s more surprised by Republican leaders’ support for Trump than he is about Trump’s praise of Putin.

“Mr. Trump rarely surprises me these days. I’m much more surprised and troubled by the fact that you have Republican officials who historically have been adamantly anti-Russian and, in fact, have attacked me for even engaging them diplomatically now supporting, and in some cases echoing, his positions,” the President said. “It’s quite a reversal. You’ll have to ask them how to explain it.”