In theory, Super Tuesday makes or breaks a U.S. presidential campaign. The day on which 24 states this year held presidential primaries is designed to demonstrate national electability. The winner on Super Tuesday is generally the front-runner for his or her party's nomination.

That logic works for U.S. Sen. John McCain of Arizona, who garnered a commanding lead in the Republican race. Sens. Hillary Clinton of New York and Barack Obama of Illinois are destined to keep slugging it out, as they neatly divided Democratic delegates. It is starting to look like they are headed toward a brokered convention in Denver in August.

Mr. McCain went into Tuesday's primaries with considerable momentum, having won previous tallies in Florida, New Hampshire and South Carolina. He compounded that lead this week, taking nine more states, including New York and California, and claiming more delegates than his other Republican rivals combined. The results leave Mr. McCain with 703 delegates, more than half the 1,191 delegates needed to win the Republican nomination. Former Massachusetts Gov. Mitt Romney has 293 delegates, former Arkansas Gov. Mike Huckabee 190, and Texas Rep. Ron Paul just 14.