WASHINGTON (AP) — President Barack Obama has been urging Colorado Democrats today to put their support and their money behind Sen. Mark Udall, who is locked in a tight re-election bid.

But Udall himself was absent from today's fund-raiser in a Denver hotel ballroom. He decided at the last minute that he would stay in Washington, rather than appear alongside the president.

His campaign said Udall needed to stay in Washington to cast his vote for Obama's nominee to head the Department of Housing and Urban Development. The nomination was overwhelmingly approved. Udall's absence is now raising fresh questions about whether Obama is more of a hindrance than a help to vulnerable Democrats like Udall who are seeking re-election this fall.

Obama told donors that Udall isn't an "ideologue," and that he doesn't agree with Obama on everything. But he called the senator "a serious person who is trying to do the right thing."

Republicans are seizing on Udall's absence from the fundraiser. His GOP rival, Congressman Cory Gardner, said Udall had been "called out on being a rubber stamp" for Obama's agenda -- and that he's now "decided to hide" in Washington instead of facing Colorado voters.

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