SEATTLE, Washington — US President Barack Obama warned Sunday that Republicans would "cripple" America, ripping into his political foes at the start of a big money campaign swing through the American west.

Obama, touting his $447 billion jobs bill amid strong political headwinds and grim prospects for the unemployment-riddled US economy, called on his supporters to brace for a "tough" 2012 election as he seeks a second term.

"This is going to be especially hard because a lot of people are discouraged and a lot of people are disillusioned," Obama said at a fundraising event in Seattle, Washington.

"I'm determined because there's too much at stake.

"The alternative I think is an approach to government that would fundamentally cripple America in meeting the challenges of the 21st Century."

The president will move on to California on Sunday night and Monday before heading home to Washington Tuesday through the vital swing-state of Colorado.

He will mix events in five cities over three days designed to hike pressure on Congress to pass his jobs bill, with a string of fundraisers where he hopes to raise millions of dollars for his campaign account.

He accused Republicans, who have controlled the House of Representatives since January, of blocking his initiatives to save the reeling economy at every turn instead of helping him fight successive crises.

"From the moment I took office what we've seen is a constant ideological pushback against any kind of sensible reforms that would make our economy work better and give people more opportunity," Obama said.

The fundraising event at the home of Jon Shirley, a former Microsoft executive, was expected to draw around 100 people at a cost of $35,800 a couple.

With his initiatives hitting a wall of Republican opposition in Congress, Obama has made a sharp rhetorical switch in recent weeks, from seeking compromise with his opponents to hammering them in populist campaign rhetoric.

At a second event in Seattle, Obama called on a crowd of supporters to "shake off any doldrums" to fire up his 2012 reelection bid, and slammed Republican claims he was indulging in class warfare.

"The only class warfare I've seen is the battle waged against the middle class," he said.

"It's about priorities," he said.

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