Because some of his friends are already on shaky ground in the next election.
“We’ve got to get it done, but I’m not drawing a line in the sand that it has to be this week versus two weeks from now,” said Sen. Claire McCaskill (D-Mo.), who faces reelection next year in a state that Trump won by more than 18 points. Other Democrats facing similar head winds echoed that sentiment, including Sens. Joe Manchin III (D-W.Va.) and Joe Donnelly (D-Ind.). Trump won those states by 42 and 19 percentage points, respectively.
Their reluctance to enact legislation protecting “dreamers” has exposed a rift among Democrats, with immigration advocates staging protests this week and accusing some Democrats of taking the party’s Latino supporters for granted.
https://www.washingtonpost.com/powerpost/democrats-unlikely-to-force-daca-vote-this-week-probably-averting-shutdown/2017/12/19/e8e59ca8-e441-11e7-ab50-621fe0588340_story.html