WASHINGTON (Reuters) - The U.S. Senate began a major, free-for-all immigration debate, its first in nearly five years, on Monday evening that could decide the fate of at least 700,000 “Dreamer” immigrants, young people brought into the country illegally years ago as children.

Late on Monday, Senator John Cornyn, the No. 2 Republican, put tight time constraints on the normally slow-moving Senate.

“It’s this week or not at all,” Cornyn said of the need for quick Senate action. Speaking to reporters, he warned that the debate had to be “wrapped up” by Thursday, before next week’s congressional recess.

Democratic Senator Dick Durbin, Cornyn’s counterpart, told reporters he hoped a combination of the Senate’s 49 Democrats and independents, coupled with 11 Republicans, could get behind a bill, propelling it to passage.

But Cornyn said tepid support among Republicans was a recipe for failure: “If they think ... they can cobble together a handful of Republicans to go along with a majority of Democrats and somehow get it past the House and get the president to sign it, I think that’s a pipedream.”

Under an order issued last year by Republican President Donald Trump, the Dreamers could be deported after March 5. That deadline looms behind the rare Senate debate, in which no single bill was to be the centerpiece and a range of ideas was in play.

By forcing the deadline on Congress with his September order, Trump drove a sharp wedge between Democrats and Republicans on an emotionally charged issue. The rhetoric around the debate was running red-hot even before it got started.

“This week we will see the horrific vision of the White House and extremist Republicans on full display ... their vision is nothing short of white supremacy,” Greisa Martinez Rosas, a Dreamer and activist told reporters on a teleconference.

On the other side, the group Advocates for Victims of Illegal Alien Crime said in a press release: “The reality is that American families are the ones suffering the most – their children killed – by illegal alien crime.”

FILE PHOTO: Protesters calling for an immigration bill addressing the so-called Dreamers, young adults who were brought to the United States as children, walk through the Hart Office Building on Capitol Hill in Washington, U.S., January 16, 2018. REUTERS/Joshua Roberts

Bridging the sometimes ugly divide between factions in the immigration debate, one that Trump himself has widened with his inflammatory statements, will be a challenge for Congress.

Despite last week’s enactment of a bipartisan budget deal, partisanship still rules in Washington. It was unclear if any immigration bill could cross the Senate’s 60-vote hurdle, let alone pass the more conservative House of Representatives.

“I just don’t know if we will have 60 votes” for anything, Durbin said.

With the 2018 congressional re-election campaigns nearing, the rhetoric was bound to escalate around the Dreamers and the program that now shields them from deportation, known as Deferred Action for Childhood Arrivals (DACA).

Started in 2012 by then-President Barack Obama, DACA gave certain young immigrants temporary protections from deportation and the ability to get work permits. It has been a target for Trump, though he seems to be torn about the Dreamers’ future.

On Monday, Trump made little effort to ease tensions. Democrats, he told reporters at the White House, have been “talking about DACA for many years and they haven’t produced.”

Trump’s September order that he would end DACA on March 5 was followed by a series of mixed signals on whether he would follow through. Under his present orders, an estimated 1,000 Dreamers a day will lose their protections beginning March 5.

Some Republicans argue that the deadline on that date has lost its force since a federal court blocked Trump from ending DACA, sending the matter before the Supreme Court.

The nine justices are due to meet on Friday to discuss how to handle the administration’s appeal. If the court decides to hear the case, an announcement could come as soon as Friday afternoon and a decision by late June.

The Senate debate was expected to center around three main approaches:

- “Dream Act” legislation to shield Dreamers who meet specific requirements and background checks. This would provide them a pathway to citizenship in up to 13 years. Supporters are open to coupling this with stronger border enforcement measures.

- The White House’s “four pillars:” Up to 1.8 million Dreamers would be protected. But in exchange for this, Trump wants funding for his U.S.-Mexico border wall, an end to a visa lottery program and tough curbs on visas for immigrants’ families.

- A bipartisan bill from Republican Senator John McCain and Democratic Senator Chris Coon blending a few such ideas.