The two-week delay in the government shutdown showdown that congressional leaders apparently have negotiated with the White House makes it less likely…and perhaps far less likely…that a shutdown will actually occur this year.
First, the longer a lame duck session of Congress goes on, the less likely that a retiring or defeated representative or senator will be around to vote at all or can be counted on to vote reliably with their leadership. They have to vacate their offices, will be losing staff, have to find a new job, have to move out of Washington and, in general, are far less focussed on being a member of Congress.
As a result, the GOP leadership will be credibly able to tell the White House that it can’t be certain of the vote count on any issue, including the one that is most likely to trigger a shutdown — the wall Trump wants built between the United States and Mexico. Because of that, Speaker Paul Ryan (R-WI) and Majority Leader Mitch McConnell (R-KY) will most likely counsel Trump not to push the issue with a shutdown.
Second, the new deadline is just four days away from Christmas. Not only will representatives and senators hate being in Washington over the holiday while a resolution of the shutdown is attempted, the bad media from furloughing federal employees and the damage it might do to the economy will be much more intense than it would have been had the shutdown occurred in the middle of December.
Third, late December will be only about two weeks before the Democrats take control of the House of Representatives and could be more logically blamed by Trump for failing to fund his wall. That should make it much easier for the president to see the political wisdom of agreeing to a short-term continuing resolution in late December that will create a confrontation with Democrats just a few weeks later.