Senators Barack Obama and Hillary Rodham Clinton competed for Democratic convention delegates across three states on Saturday, locked in a marathon struggle for the party's presidential nomination after nationwide contests this week failed to produce a clear front-runner. Republican Mike Huckabee said he won't quit the presidential race even though Arizona Sen. John McCain appeared to all but lock up the nomination after winning hundreds of delegates in the party's 21 contests on Super Tuesday. In the first contest of the day, Huckabee easily won the Republican caucuses in Kansas, reflecting McCain's difficulties in shoring up support from conservatives - the party's core constituency - despite his status as the presumptive nominee. With nearly 80 percent of the vote counted, the former Arkansas governor had 62 percent of the vote, compared to 22 percent for McCain, and 11 percent for libertarian-leaning Texas Rep. Ron Paul. Thirty-six delegates were at stake.