(CNN) The history of government shutdowns -- and the polling on this shutdown in particular -- suggested that Democrats were poised to benefit politically from the shuttering of the federal bureaucracy.

And then, suddenly on Monday afternoon, Democrats gave in , with all but 16 of their 48 members voting to reopen the government with a three-week continuing resolution and a vague promise from Senate Majority Leader Mitch McConnell that they would get a fair hearing in their efforts to extend the DACA immigration program.

Why?

Good question! And one that many liberals within the party -- up to and including the half-dozen or so Democrats in the Senate planning runs for president in 2020 -- are asking in the wake of the Democrats' capitulation. (Read my winners and losers from the shutdown here .)

The answer -- I think -- is that red-state Democrats up for re-election in 2018 panicked. As I've noted many times in this space, there are 10 Democrats running for re-election this fall in states Trump won in 2016 -- including five in states where the President won by double digits.

For them, the shutdown was rapidly being painted as the Democratic Party taking their ball and going home because Republicans wouldn't agree to a deal for citizenship for undocumented immigrants. (I'm not saying this is what the reality of the debate reflected -- only what the perception was.)

In many of these Senate seats held by Democrats -- North Dakota, West Virginia, Indiana, Missouri -- that positioning was untenable. And so they put pressure on Senate Minority Leader Chuck Schumer -- who helped elect many of these same members as chairman of the Democratic Senate campaign arm -- to get the best deal he could, reopen the government and declare victory.

Which is what Schumer tried to do. But the facts of the deal -- a three-week CR with no guarantee of a clean DACA vote -- belie that claim of a Democratic win. As do comments made by Democrats from Congressional Black Caucus Chairman Cedric Richmond (Senate Democrats "are getting their butts kicked") and California Sen. Kamala Harris ("Listen, I'm disappointed with a conversation that suggests a false choice: You either fund the government or you take care of these DACA kids. We can do both.")

Could this be short-term pain for long-term gain? Sure. But remember that even if Schumer gets his promise out of McConnell for a DACA vote and even if it passes the Senate, the Republican-controlled House and White House await. And it's hard to see a Senate deal surviving those two gauntlets.