Despite another landslide loss to rival Sen. Hillary Rodham Clinton (D-N.Y.) in Kentucky earlier in the evening, Obama further strengthened his hand with the Tuesday night win.

Obama aides have said repeatedly in recent days that the Illinois senator would not declare victory Tuesday night, focusing instead on the mathematical landmark in a speech from Iowa — the state that launched his run to verge of the nomination almost six months ago.

The Obama campaign has in recent days appeared wary of offending Clinton supporters by suggesting that the former first lady should withdraw from the race. Instead, Obama has trained his fire on presumptive Republican nominee Sen. John McCain (Ariz.).

For her part, Clinton has vowed to continue the fight even as she has blunted her once-intense criticism of Obama. Her big win in Kentucky, however, continued to highlight the problems Obama has had with white, rural voters.

A week earlier, Clinton beat Obama by 41 points in West Virginia.

Regardless of the two big losses, superdelegates have been moving to Obama’s column at a far greater pace than they have moved to Clinton’s.

Obama secured the support of two high-profile superdelegates over the past week in Sen. Robert Byrd (W.Va.) and former North Carolina Sen. John Edwards.