Representative Paul D. Ryan used his convention speech on Wednesday to fault President Obama for failing to act on a deficit-reduction plan that he himself had helped kill. He chided Democrats for seeking $716 billion in Medicare cuts that he too had sought. And he lamented the nation’s credit rating — which was downgraded after a debt-ceiling standoff that he and other House Republicans helped instigate.

And Mitt Romney, in his acceptance speech on Thursday night, asserted that President Obama’s policies had “not helped create jobs” and that Mr. Obama had gone on an “apology tour” for America. He also warned that the president’s Medicare cuts would “hurt today’s seniors,” claims that have already been labeled false or misleading.

The two speeches — peppered with statements that were incorrect or incomplete — seemed to signal the arrival of a new kind of presidential campaign, one in which concerns about fact-checking have been largely set aside.

In recent weeks, the Romney campaign has broadcast television advertisements leveling the widely debunked assertion that Mr. Obama had gutted the work requirements for welfare recipients. The Obama campaign, for its part, ran a deceptive ad saying that Mitt Romney had “backed a bill that outlaws all abortion, even in case of rape and incest,” although he currently supports exceptions in cases of rape, incest or when the life of the mother is at risk.