President Obama underestimated the effect of his own plan to provide limited amnesty to young illegal immigrants, and the clerical error — as was the case when he put a price tag on Obamacare — was in his favor.

“As many as 1.76 million unauthorized immigrants who were brought to the United States as children could potentially be eligible for a grant of relief from deportation,” the Migration Policy Institute reported this week, as Obama’s effort to implement the DREAM Act by choosing not to enforce current laws goes into effect. Obama and his Department of Homeland Security estimated that 800,000 illegal immigrants would benefit from this policy — about half what MPI now says.

“There is little that’s clear about the President’s jobs agenda but it’s crystal clear that he has placed opportunities for illegal immigrants to work in the U.S. at the top of his list,” House Judiciary Chairman Lamar Smith, R-Texas, said in a statement yesterday. “How can the Administration justify implementing a fraud-ridden program that will deprive Americans of jobs and cost taxpayers? . . . . With this track record, it’s looking more likely that even President Obama may lose his job in this economy when Americans go to the polls this November.”

Flashback to 2009 and 2010: When Obama pushed health care reform (the bill he passed rather than immigration reform), he said it would cost about $900 billion. The Congressional Budget Office reported in March that Obamacare is twice as expensive, costing $1.76 trillion over ten year. (The true cost is even higher, but the CBO calculations cannot account for the double-counting in the health care bill.)

MPI, unlike the CBO, is not a government entity, but it based its estimates of how many people would qualify on new information released by DHS in August.