When General Motors tells a presidential campaign that it is engaging in “cynical campaign politics at its worst,” that’s a pretty good signal that the campaign has crossed a red line and ought to pull back. Not Mitt Romney’s campaign. Having broadcast an outrageously deceitful ad attacking the auto bailout, the campaign ignored the howls from carmakers and came back with more.

Mr. Romney apparently plans to end his race as he began it: playing lowest-common-denominator politics, saying anything necessary to achieve power and blithely deceiving voters desperate for clarity and truth.

This started months ago when he realized that his very public 2008 stance against the successful and wildly popular government bailout of G.M. and Chrysler was hurting him in the valuable states of Ohio and Michigan. In February, he wrote an essay for The Detroit News calling the bailout “crony capitalism on a grand scale” because unions benefited and insisting that Detroit would have been better off to refuse federal money. (This ignores the well-documented reality that there was no other cash available to the carmakers.)

When that tactic didn’t work, he began insisting at the debates that his plan for Detroit wasn’t really that different from President Obama’s. (Except for the niggling detail of the $80 billion federal investment.)