Republican and Democratic senators in the “gang of eight” immigration reform group gave Marco Rubio an earful at a private meeting this week, telling him they were frustrated with his public embrace of overly conservative border security measures and his failure to adequately communicate with them over strategy, which they said was putting reform at risk, I’m told.

The details of the private meeting on Wednesday – which were shared with me by a source familiar with the episode — shed new light on the delicate behind the scenes strategic calculations the gang of eight is making as it seeks to navigate its proposal past conservative opposition through the Senate. The meeting hints at the true nature of the collective kabuki that the gang of eight is engaged in as it seeks to create just enough space to the right for Republicans to embrace the bill — without moving it so far to the right that it alienates Democrats.

Publicly, Senators have mostly remained mum as Rubio has flirted with conservative demands for more border security. But in the private meeting, Republican and Democratic senators in the gang of eight expressed “frustration” with Rubio over the manner in which he publicly embraced the John Cornyn amendment, which mandates hard border security “triggers” as a precondition for citizenship in a manner Dems find unacceptable, the source tells me.

In particular, they complained that Rubio’s manner of endorsing the Cornyn plan had made it easier for other GOP Senators whose support is deemed gettable on the gang of eight compromise to instead latch on to something far more conservative (the Cornyn plan) that the rest of the gang will not support. As feared, uncommitted Republican Senators are beginning to clamber aboard the Cornyn “hard trigger” express.

“The senators were frustrated because they felt like Rubio’s mixed signals on the Cornyn amendment were falsely raising expectations among gettable Republicans about the types of changes that are acceptable on border security,” the source tells me. “The Senators told Rubio that the Cornyn amendment is going nowhere, and the sooner that is clear to everyone, the more quickly we can move to other, more acceptable proposals.”

Senators on both sides also complained that Rubio had failed to give them a “heads up” before publicly embracing the Cornyn plan. “They asked for better communication from him,” the source says.

The meeting, which was called to discuss floor strategy generally, included all eight gang members, including Republicans Lindsey Graham, John McCain, and Jeff Flake, and Dems Chuck Schumer, Dick Durbin, Robert Menendez, and Michael Bennet.

All of this goes directly to just how delicate a dance these Senators are engaged in. The gang of eight senators understand that Rubio needs to be given the space to support amendments that the gang will never support, in order to shore up his conservative credentials, which is necessary for him to be able to attract conservative support for the final Senate plan that emerges with the gang’s blessing. But senators in the gang want Rubio to consult with them privately as he does so, so they are not blindsided and can calibrate strategy accordingly. And they are wary of him increasing expectations among other Republicans that the gang will move further to the right than they are prepared to go — which could ultimately make it harder to win GOP support in the end.

************************************************************

UPDATE: A Rubio spokesman declined to comment for this story, citing a policy against publicly discussing private meetings.

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