Mitt Romney tightened his grip on the Republican presidential nomination Tuesday night, sweeping primaries in Wisconsin, Maryland and Washington, D.C., with time left over to swap charges with President Barack Obama.

As Mitt Romney looked for a sweep in Tuesday’s three Republican primaries to tighten his grip on the party’s nomination, President Barack Obama criticized the GOP front-runner by name in a campaign ad for the first time, signaling that he too thinks the nomination race is all but over.