The president suggested he would hold off introducing his own immigration bill as long as bipartisan Senate negotiations were proceeding apace — until his own immigration bill mysteriously leaked precisely as bipartisan Senate negotiations were proceeding apace.

A naked political maneuver and a blunt warning to Republicans: Finish that immigration deal in Congress or I’ll propose something I know you can’t accept and flog the issue mercilessly next year to win back the House.

Marco Rubio, a chief architect of the Senate bill, called Obama’s alternative dead on arrival.

He protests quite a lot — especially because on the single most important issue — instant amnesty — there is no real difference.

Rubio calls it “probationary legal status.” Obama uses the term “lawful prospective immigrant.” Both would instantly legalize the 11 million illegal immigrants living here today. The moment either bill is signed, the 11 million become eligible for legal residence, the right to work and an end to fear of deportation.

Call the status probationary or prospective but, in reality, it is permanent. There is no conceivable circumstance (short of criminality) under which the instant legalization would be revoked.

This is bad policy. It repeats the 1986 immigration reform that legalized (the then) 3 million while promising border enforcement that was never carried out. Which opened the door to today’s 11 million. And to the next 11 million as soon as the ink is dry on this reform.

The better policy would be enforcement first, followed by amnesty. Yes, amnesty. But only when we have assured that these 11 million constitute the last cohort.

How to do that? With three obvious enforcement measures: (a) a universal E-Verify system by which employers must check the legal status of all their hires, (b) a system for tracking those who have overstayed their visas, and (c) closure of the southern border, mainly with the kind of triple fence that has proved so successful near San Diego.

If legalization would go into effect only when these conditions are met, there would be overwhelming bipartisan pressure to get enforcement done as quickly as possible.

But there appears to be zero political will to undertake this kind of definitive solution. Democrats have little real interest in border enforcement. They see a rising Hispanic population as the key to a permanent Democratic majority. And Republicans are so panicked by last year’s huge loss of the Hispanic vote that they have conceded instant legalization.

Hence Rubio’s fallback. He at least makes enforcement the trigger for any normalization beyond legalization. Specifically, enforcement is required before the 11 million can apply for a green card.

A green card is surely a much weaker enforcement incentive than is legalization. But it still is something. Obama’s proposal, on the other hand, obliterates any incentive for enforcement.

Obama makes virtually automatic the eventual acquisition of a green card and citizenship by today’s 11 million. The clock starts on the day the bill is signed: eight years for a green card, five more for citizenship. It doesn’t matter if the border is flooded with millions of new illegal immigrants (anticipating yet the next amnesty).

As for Obama’s enforcement measures themselves, they are largely mere gestures: increased funding for border control, more deportation judges, more indeterminate stretching of a system that has already demonstrably failed.

And remember: Non-implementation of any of this has no effect on the path to full citizenship anyway. The Rubio proposal at least creates some pressure for real enforcement because green card acquisition does not take place until the country finally verifies that its borders are under its control. True, a far weaker incentive than requiring enforcement before legalization. But that fight appears to be totally lost.

In the end, the only remaining vessel for enforcement is the Rubio proposal. It is deeply flawed and highly imperfect. But given that the Obama alternative effectively signs away America’s right to decide who enters the country, the choice between the two proposals on the table today is straightforward.