Rubio plunges into immigration debate head first

But it's significant as the Democrats needed the lofty threshold of 60 votes to move on to the border package that is in line with their priorities and basically those of the White House although it would spend $1 billion less than what President Barack Obama wants.

Most in Rubio's caucus opposed, including fellow potential White House hopefuls Rand Paul of Kentucky and Ted Cruz of Texas. And it all took place as House leaders reworked their version in an uncertain bid to attract conservative support to address the situation most consider a humanitarian crisis.

The Rubio vote carries unique significance for him, regardless of the proposal's outcome.

That's because his aspirations for higher office took a big hit in the Republican Party over his central role in drafting and then voting for comprehensive immigration reform last summer. He later moved away from the legislation, but it was too late, politically.

Vocal and influential conservatives panned the measure over their claims it would not secure the southern border and would only create amnesty for some 11 million undocumented immigrants already in the country.

The legislation stalled in the GOP-led House, as did Rubio's standing with the right wing of the party. Conservative views are paramount in the presidential nominating contest, and they simply didn't like what the son of Cuban immigrants had done.

So after all that, and a lot of effort since to rebuild his standing with conservatives, why did he cast his lot with Democrats on an immigration vote again?

"I voted to move to the Senate border bill so that we would have the opportunity to vote on and pass amendments that would achieve real reforms," Rubio wrote in a statement.

He also said he would not support a final bill unless the Democratic-led chamber did two things that Republicans want: Change a 2008 law to make it easier to deport young migrants from Central America as a deterrent and toss parts of an Obama administration program that eases deportation of other immigrants in the United States illegally.

Most Democrats don't want either change, but Republicans blame the influx of young immigrants from El Salvador, Guatemala and Honduras on what they contend are flawed immigration policies. The message, they say intended or not, is that it's easier to immigrate.

This is the first time in the border crisis debate that Rubio has inserted himself in a significant way.

While he has given numerous interviews about the nearly 60,000 minors -- many of them unaccompanied -- who have crossed the border in the past 10 months, he has not been instrumental in crafting emergency legislation in Congress to address it.

Rubio's vote on Wednesday certainly carries some risk, judging by conservative responses to more Republican-friendly legislation in the House.

Erick Erickson, editor of the conservative blog RedState, wrote Thursday that the slimmed down, $659 million House proposal is actually "inexcusable."

His problem with it is that it gives money to Obama to disperse to border and other immigration programs without imposing the changes to immigration policy Republicans want immediately.

While Rubio's willingness to move forward could be unpopular among conservatives, enough lawmakers on both sides of the aisle and in both chambers are concerned about leaving town Friday for the month of August without doing anything about the border crisis.

House members and senators will be spend the rest of the summer amid constituents back home where polls show immigration overall is especially on the minds of voters.

In a recent CNN/ORC survey, 39% say it's extremely important for Obama and Congress to deal with illegal immigration in general, up 10 points from last year.

"That means that immigration is the only issue tested that has grown significantly more important to the public in the past year," CNN Polling Director Keating Holland said.

House GOP seeks cover with slimmer border bill