Mitt Romney cruised to victories Tuesday in Wisconsin, Maryland and the District of Columbia, adding to his widening delegate lead over the rest of the Republican presidential field.

Former Pennsylvania Sen. Rick Santorum trailed the GOP front-runner by a wide margin in Maryland and several thousand votes in Wisconsin, after he failed to get on the ballot in the nation's capital. Ron Paul and Newt Gingrich lagged far behind in all three primaries.

In Wisconsin, with 99% of precincts reporting, Mr. Romney led with 44%, followed by Mr. Santorum with 37%, Mr. Paul with 11% and Mr. Gingrich with 6%. With all precincts reporting in Maryland, Mr. Romney had 49%, Mr. Santorum 29%, Mr. Gingrich 11% and Mr. Paul nearly 10%. Mr. Romney took 70% of the vote in D.C.

With three weeks before candidates face another batch of voters, Tuesday's contests mark a clear inflection point in a race that has entered its fourth month and is now tipping further in favor of the former Massachusetts governor.

Mr. Romney's latest wins come as Republicans increasingly are closing ranks behind him in the hopes of expediting the fall showdown with President Barack Obama. The run-up to Wisconsin brought Mr. Romney endorsements from Florida Sen. Marco Rubio and Rep. Paul Ryan of Wisconsin, two lawmakers often mentioned as possible running mates.