“He joined the Democrats in killing Grassley’s amendment that would require border security before the amnesty.”
And without that I don’t think it will pass. Do You?
Sabotage.
You talk as though Rubio is withdrawing his support for this bill because it's been poisoned. He hasn't sabotaged anything. He's been out there day and night, stumping for this crap sandwich all across the country, and in front of every microphone he could find.
The first amendments that come along that make this thing even slightly palatable, and he votes against them with the Democrats. By your logic, the Dems voted against the amendments for the same reason.
Sorry, but that fails.