So when Sen. Marco Rubio disagreed with the prevailing assumption that the Gang of Eight immigration bill had at least the 60 votes necessary to overcome a filibuster by his GOP colleagues, he knew something the rest of us didn’t know: he was counting himself as a “no” vote. And it turns out he’s been working behind the scenes with John Cornyn (who voted against the bill in the Judiciary Committee) to draft an omnibus conservative “poison pill” amendment to the bill that if passed would by all accounts unravel the whole bipartisan coalition supporting comprehensive immigration reform. Here’s Wonkblog‘s take on the Cornyn (or should we say Cornyn/Rubio?) amendment:

His amendment would require 100 percent operational control of the Southern borders and that 90 percent of illegal border crossers be apprehended. It would also require 100 percent border surveillance, or situational awareness, of each one-mile segment of the Southern border and installment of a national E-Verify system before registered immigrants can pursue green cards.”

That sure sounds as if no one is ever getting a green card. That level of operational control — unless operational control is defined quite far down — is nearly impossible.

In taking this impressively treacherous step against a bill he was happy to identify himself with when it was working for him politically, Rubio is hiding behind the argument that the bill needs to be toughened up to be acceptable to the House. I don’t know if he’s going to perpetually pretend he’s never heard of House-Senate conference committees, or wasn’t aware of the immigration reform strategy of getting a good, strong pro-reform bill out of the Senate to put pressure on House troglodytes. It’s also hard to tell if this was Rubio’s devious plan all along, or if he’s panicking over the damage the Gang of Eight bill has inflicted on his 2016 presidential ambitions.

The latter theory finds additional support in Rubio’s interestingly timed announcement yesterday that he’s introducing a constitutional amendment to overturn the Supreme Court’s validation of the individual mandate as imposed by the Affordable Care Act. This entirely meaningless base-pleasing gesture is an indication that the junior senator from Florida is worried about keeping his right flank covered.

UPDATE: Conservative reporter Byron York, a foe of the Gang of Eight bill, speaks for many on both sides of the issue in expressing amazement over Rubio’s apparent flip-flop:

Rubio’s turning on his own bill would be an extraordinary turn of events. After playing a major role in drafting the legislation, Rubio has been its public face since then, making countless appearances on television, radio, and in print to gather support for the legislation. What has changed that would mean he would not vote for his own bill? If anything, the security measures in the bill were slightly strengthened in the Senate Judiciary Committee.

Ed Kilgore

Ed Kilgore is a political columnist for New York and managing editor at the Democratic Strategist website. He was a contributing writer at the Washington Monthly from January 2012 until November 2015, and was the principal contributor to the Political Animal blog.