Consider two quotations, the first engraved in modern history and the other a week old, and ask yourself what they have in common:

“This morning I had another talk with the German chancellor, Herr Hitler, and here is the paper which bears his name upon it as well as mine. . . . I believe it is peace for our time.”

And then: “I think I’d be able to get along with him. . . . If he says great things about me, I’m gonna say great things about him. I’ve already said he is really very much of a leader.”

The first quotation, of course, is from Neville Chamberlain in September 1938, at the time of the Munich Agreement that sought a peaceful accommodation with Germany, allowing annexation of the Sudetenland in Czechoslovakia. The second, from last week’s NBC forum, is Donald Trump’s encomium for Russian President Vladimir Putin, who has been attacking the United States and its allies in Ukraine, Syria and cyberspace.

The name given to Chamberlain’s policy was “appeasement,” and it has come to be seen as one of the catastrophic mistakes of history. But it’s easy to understand why accommodation with the German dictator seemed sensible at the time. The nightmare of war was still fresh for the British public. People were worried about jobs. Britain was exhausted and demoralized; Chamberlain judged that his country wasn’t ready for another war.

On Sept. 7, during a town hall event hosted by MSNBC, Republican presidential candidate Donald Trump stated he would have “a good relationship” with Russian president Vladimir Putin. It wasn’t the first time he's been friendly towards him. (Adriana Usero/The Washington Post)

Political analogies are often unfair, especially ones that invoke the overused Munich parallel. But this one is worth considering: The problem with Trump isn’t (as some critics have argued) that he’s a reckless and potentially genocidal aggressor. No, the danger is that he’s precisely what he says he is — a dealmaker who thinks he could craft agreements with despots that could bring peace and security.

Trump seems to see commitments made to smaller states as expendable in the process of making deals with the big guys. When he linked U.S. willingness to defend the Baltic states and other NATO allies to what they pay into the alliance, it was a Chamberlain-esque emphasis on national self-interest, as opposed to sticking your neck out for possibly undeserving little guys.

This idea of reaching agreements with Putin’s Russia isn’t crazy, any more than was Chamberlain’s desire to escape war in 1938. And Trump actually deserves credit for raising this issue early in the Republican primary debates. But any such negotiation must be done carefully and unsentimentally, without the mutual self-congratulation that has characterized Trump’s comments about Putin. Secretary of State John F. Kerry is pursuing his own version of a deal with Putin, in the Syria agreement announced Friday night. Kerry has concluded that there’s no way to reduce the violence in Syria without working with Moscow. But Kerry has negotiated very cautiously, with the Pentagon looking over his shoulder at each detail before he signs off. He has specified what the Russians will have to deliver, in terms of calm on the battlefield and grounding the Syrian regime’s air power, for this deal to work.

When U.S. leaders think about negotiating with Russia, they need to be sure their model is John F. Kennedy in the Cuban Missile Crisis, rather than Chamberlain at Munich. Appeasement happens when other nations are treated as sacrificial pawns, and when the adversary is sentimentalized. These are precisely the areas where Trump’s comments have been worrying.

One of the most useful cautions about dealing with Putin’s Russia was offered by Hillary Clinton in a memo she sent President Obama in January 2013, just before she left office as secretary of State. In her memoir “Hard Choices,” she recalled: “In stark terms, I advised the president that difficult days lay ahead and that our relationship with Moscow would likely get worse before it got better. . . . Putin was under the mistaken impression that we needed Russia more than Russia needed us.”

Russia has been pushing the envelope of power at all its seams. The United States needs to establish clear limits — by negotiations, where they’re possible, and also by showing that it’s willing to use military power, if necessary. That’s precisely the tightrope that Kerry has been trying to walk — seeking more military leverage against Moscow, even as he negotiates. The test of Kerry’s seriousness will be his willingness to walk away from the Syria deal if Russia doesn’t deliver.

We’re not in Neville Chamberlain territory, not even close. But this is a slippery slope, not just for Trump, but for the United States.

Read more from David Ignatius’s archive, follow him on Twitter or subscribe to his updates on Facebook.