(CNN) The Senate will embark on a free-wheeling immigration debate this week, testing the limits of whether there is still a political center on the contentious issue in the era of President Donald Trump and if a deal can be reached in a span of a few days.

The Senate voted Monday evening to advance that debate, the first step in potentially protecting hundreds of thousands of undocumented immigrants brought to the US illegally as children from deportation, but pressure from both the left and right could make it harder than ever to achieve something on immigration.

"This President ran on the most outspoken, anti-immigration platform of any presidential candidate in modern history. He said things during the course of the campaign, he's done things since he was elected President ... and made it clear that this is the bedrock of his base support," Sen. Dick Durbin, the Democratic whip, told reporters Monday evening. "We hadn't faced something quite that organized and specific when we took this up five years ago. This has made it much more difficult."

Unlike five years ago, when the Senate debated comprehensive immigration reform on the floor of the Senate, the politics of the moment have been complicated by not only a President who made building a border wall and deporting immigrants the centerpiece of his campaign, but a Democratic base that is demanding more than ever that its members hold the line against the President.

Another complicating factor? Members and aides tell CNN that the debate is only expected to last a week, a tight deadline for a congressional body that relies on unanimous cooperation and is prone to dilatory tactics.

Read More