Today the Senate voted 68-32 to end debate on the gang of eight immigration bill, and it’s headed this afternoon for final passage by a sizable margin. The margin of victory – in what will be widely trumpeted by Dems as a historic vote — means the spotlight will suddenly swing rather dramatically on to the House.

One thing worth watching: What will Paul Ryan do?

Today Speaker John Boehner actually drew a sharper line than before in ruling out any vote on an immigration bill that lacks the support of a majority of House Republicans. He said such a bill would not get a vote even if it emerged from Senate-House conference negotiations. Boehner appears to be continually caving to conservative demands to rule out letting anything that might pass with Dem support to even get to the House floor.

In this context one key question is whether Ryan — who supports immigration reform — will stand up to conservatives in his own party who want to push the bill so far to the right that it ends up being unacceptable to Dems, and who are insisting that nothing that looks even remotely like the Senate bill must ever get a House vote.

Ryan has a lot at stake here. He is expected to run for president in 2016. But if House Republicans take the blame for sinking immigration reform’s hopes, the death of reform could be a larger general election albatross for him (the GOP primary is another matter) than other 2016 presidential hopefuls, given his leadership role in the body that killed reform.

On immigration, Ryan stands as an interesting contrast to Marco Rubio, another pro-reform Republican with 2016 ambitions. After playing it cute for months by continually hinting that he’d bail on reform if it wasn’t made conservative enough, Rubio finally did stand up to conservatives by effectively casting his lot with reform that Dems could support, taking a ton of criticism from the right in the process.

Rubio seems to be betting that being on the side of constructive problem solving on immigration — even if it means taking heat from conservatives — is the best place to be heading into 2016. Will Ryan — who could also exercise leadership on the issue, given the tremendous credibility with conservatives he enjoys as architect of the party’s dominant fiscal vision — do the same?

Ryan is trying to play both sides right now, too. Today in an interview with Sean Hannity he pushed back on conservative notions that a path to citizenship is “amnesty,” arguing it’s actually an effort to get undocumented immigrants “right with the law.” But he also reiterated opposition to bringing up the Senate bill and insisted the final product must have “real triggers on the border.”

If by “real triggers” Ryan means something like what was in the Cornyn amendment, that is a nonstarter for Dems, since those are all about nixing citizenship. So at some point, Ryan is going to have to take a stand on behalf of a real path to citizenship without the hard triggers that are certain to sink reform’s hopes, and accept the need for Republicans to find a way to embrace something that looks like the Senate bill. Or he’ll be a leading member of the crew that will take all the blame for sinking a historic opportunity – after it passed the Senate by a wide margin — to finally achieve a path to citizenship for millions and dramatically increased border security. How would that work out for anyone who is eying the 2016 general election electorate?

Greg Sargent writes The Plum Line blog, a reported opinion blog with a liberal slant -- what you might call “opinionated reporting” from the left.