One reason Rubio has looked so good thus far, in other words, is that his biggest and most obvious weakness hasn't been on the table. That's a lucky break, but it's hard to see how it will last. If by the next debate Rubio has succeeded in clearly displacing Jeb Bush as the establishment favorite, then the incentives for Cruz and Trump (or even Christie or Fiorina) to start lighting into Rubio on immigration get a lot bigger. But as Cruz himself outlined to Shane Goldmacher, his current plan is to focus on consolidating the vote that he is currently splitting with Trump and Ben Carson and only later turn on whomever the strongest establishment-friendly candidate will be.
As the race for the Republicans' presidential nomination started to take shape, there were plenty of reasons to be skeptical of Sen. Marco Rubio's (R-Fla.) chances. For example, he's a career politician who's never run anything. He has no real accomplishments. He's developed no areas of policy expertise. Rubio gives a nice speech, but there's ample reason to question whether he's prepared for national office.
It's quite easy to imagine, however, Republican voters overlooking all of this. Indeed, these truths may be a problem for a general-election audience, but there's no reason to believe any of them would be a deal-breaker in GOP primaries and caucuses.
All of which brings us to the one problem Rubio may not be able to dismiss with ease: comprehensive immigration reform.
If I were a Republican presidential candidate, and I were at all worried about Rubio, I'd probably repeat one talking point every minute of every day: "Marco Rubio partnered with liberal Democrats to write Obama's 'amnesty' bill." For the GOP base, the bipartisan immigration reform package is truly despised -- it's right up there with "Obamacare" -- and yet one of the party's leading presidential candidates is one of the bill's authors.
I don't understand why this simple, straightforward detail isn't dominating the Republican race. I don't mean that in a rhetorical sense; I mean I literally don't understand it. Shouldn't candidates like Ted Cruz and Donald Trump be screaming this from the hilltops?
Vox's Matt Yglesias took a look at this dynamic today, arguing that the "chickens will (probably) come home to roost."
At this point, the limited areas of disagreement between the competitive candidates will be extremely important. Candidates like Rubio and Cruz agree on practically everything, making it all the more important that the former aligned himself with Democrats on immigration while the latter fought to kill the bill.
Yglesias added, "It hasn't hurt him thus far because it simply hasn't been tried. But it's nearly inconceivable that Rubio can keep coasting much longer without facing his core vulnerability."
It's worth emphasizing that Rubio has no doubt memorized the script on what to say when this comes up. The Florida Republican will assure his party's base that he now opposes the bill he helped write in the last Congress, and he's already gladly betrayed his former allies on what was supposed to be his signature issue. Never mind what he supported in 2014; he wants the focus on his brand new position rolled out in 2015.
Whether such an argument will be persuasive remains to be seen, but if the race for the nomination comes down to Cruz vs. Rubio -- a scenario I consider fairly likely -- the only major area of disagreement between them will be immigration, and the Texan will have a potent message to share.