Tuesday's primary results lock things up on the Republican front. Senator John McCain swept all four contests.

The primaries in Ohio, Texas, Rhode Island, and Vermont seal the deal for McCain's nomination as the Republican candidate, pushing out Mike Huckabee and Ron Paul.

Mike Huckabee officially stepped down after the results were released.

McCain says clinching the nomination is "a humbling experience."

Republicans won't officially nominate him until early September at the 2008 National Republican Convention in Minnesota.