This is an updated version of my post earlier on August 13. At least one key pro- immigration reform Republican is taking the possibility of Plan B seriously. POLITICO reports on August 13 that GOE member Senator Marco Rubio (R-FL) is warning that if House Republicans continue to block CIR, President Obama may legalize 11 million unauthorized immigrants by executive order.
See POLITICO:Marco Rubio warns of immigration executive order August 13.

In that case, from a Republican perspective, there would be the worst of both possible worlds - legalization without the strict border security and e-verify enhancement measures that are in the Senate-passed CIR bill.

POLITICO quotes Rubio as follows:

"Unless we're going to try to try to round up and deport 11 million people - something that not even the most vociferous opponent of the [Senate] bill proposed, then we are going to have to at some point address this issue...We can't leave, in my mind, the way it is. Because I think a year from now we could find ourselves with all 11 million people here legally under an executive order from the president, but no E-Verify, no more border security, no more border agents, none of the other reforms we definitely need."

In other words, Rubio seems to be saying that by trying to kill CIR, anti-reform Republicans are cutting off their noses to spite their faces. But how many congressional Republicans are interested in listening to a voice of reason and sanity on immigration reform coming from their own party, instead of pursuing the self-destructive "self-deportation" fantasy which helped them lose the 2012 presidential election?

Some of the early reactions I have seen to Rubio's comment appears to assume, optimistically, that if the president legalizes 11 million people by executive order, anti-immigrant Republicans will roll over and play dead, having learned their lesson.

But there is another possible, if not even more likely scenario - that the Steve King, bigoted, anti-immigrant wing of the GOP would try to use this as an excuse for impeachment proceedings in the House against Obama. Already, there is no shortage of calls for impeaching the president among the right wing Republican lunatic fringe, over everything from Benghazi (remember that?) to the IRS "scandal" to his birth certificate.

There are also calls for his impeachment over DACA. See, for example an anonymous August 7 post on a site called examiner.com entitled: Should Obama be impeached over his refusal to enforce the law?

If the president attempts to legalize 11 million people through executive order, or even threatens to do this as a bargaining chip to try to goad the House into action over CIR, it may give the Republicans just what they need to convince a great number of Americans that the battle against reform is really about protecting the country against an abuse of executive power, rather than preserving racism and discrimination against minorities.

If CIR fails, Republicans would have an additional argument that by granting an executive order for legalizing 11 million unauthorized immigrants, instead of "only" a million or so DREAMERS, the president had "defied" the will of Congress on a truly massive scale.

Does anyone think for a moment that anti-immigrant Republicans, fresh from a victory over reformers in killing CIR, would let that victory be snatched away from them by executive order without taking action? Anyone who thinks that must also think that Marco Rubio speaks for most Republicans on immigration, rather than being far more rational than most of his party.

One way that President Obama might be able to issue an executive order and also take with wind out of the sails of impeachment would be to issue an executive order for both halves of CIR - legalization and enhanced border security/e-verify.

Politically, it might be very hard for Republicans to try to impeach him over an executive order which carries out many of their most important enforcement goals.

But the most important question of all may be: would the President have the courage to risk impeachment by trying any type of Plan B executive order? His actions as Deporter in Chief for more than a million people during his first term do not offer much encouragement in that direction.