Over the past 24 hours, the immigration reform effort has gotten two key GOP shows of support from Sen. Kelly Ayotte (R-N.H.) and the outside group Crossroads GPS.

But even as it appears on the surface that the bill is inching toward passage as the Senate takes it up this week, the support of Ayotte and Crossroads actually demonstrate what a tough path the bill faces.

While Ayotte's support is notable and means the bill is approaching the 60 votes it needs to override a filibuster in the Senate, the way in which she announced her support says a lot.

An e-mail from Ayotte explaining her decision clocked in at more than 2,800 words, and it linked to a separate "op-ed" on her Web site that made the same case. Any time a politician needs nearly 3,000 words to justify a position, you can tell it's dicey. (Ayotte, of course, was a prime target of gun control groups after her vote against expanded background checks, so perhaps she's just trying to get ahead of story this time around.)

As for Crossroads, while it announced its broad support for the effort, it did so with several apparent caveats. The group said it would like amendments to "secure the border, allow for high-skilled immigration, prohibit eligibility for welfare and Obamacare benefits, put undocumented immigrants at the back of the line, and replace the current chain migration system to one that is merit-based."

That's a lot of asks, and each of those amendments will be contentious. In addition, Democrats contend that adding them to the bill may constitute a "poison pill" that would jeopardize Democratic support for the bill.

Ayotte's and Crossroads' support come on the heels of two other notable events in the immigration debate last week. The first was the House's passage of a bill that would overturn President Obama executive order exempting young illegal immigrants from deportation — similar to so-called DREAM Act legislation. And the second was Sen. Marco Rubio (R-Fla.) saying he wouldn't support the immigration bill (a bill he helped craft) without tougher border security measures.

The House vote signals that congressional Republicans aren't afraid to take votes that may jeopardize their standing with Latinos. Indeed, the vote last week was essentially a symbolic measure with no chance of passage in the Senate, but it still got the support of 221 out of 227 Republicans who voted. If they're voting for that, why wouldn't they also vote against a path to citizenship?

And Rubio's position, while ostensibly intended to help create a bill that can actually pass in the House, shows just how uncertain a proposition that is. The fact that Rubio doesn't think a compromise that he previously agreed to can pass muster in the lower chamber without some changes shows how Congress is really going to have to thread the needle on this one.

Crossroads sees that too, which is why its support included as many provisos as it did.

Ayotte, Crossroads and Rubio are all sticking their necks out, to some degree, for immigration reform, but the way in which each of them have demonstrated their support points to the very difficult path ahead.