SAN FRANCISCO — US President Barack Obama forcefully argued Tuesday that he had honored the passionate demands for change that swept him to the White House, including in the operation that killed Osama bin Laden.

On a western campaign swing, the president challenged supporters to show their commitment to his reelection bid, and argued he had done more than half of what he promised to do in his 2008 election campaign.

"Change is possible. We've made change, and we've made it because of you. And so the question is: How committed are you going to be to continue this process?" Obama said at a fundraiser in San Francisco, California.

"You know, I keep a checklist in my drawer of my campaign promises ... and we've gotten about 60 percent done so far -- in three years, but I need another five to get the other 40 percent done."

Some liberal voters have soured on Obama in recent years, feeling that he has not lived up to campaign promises or not been sufficiently vociferous in standing up to his Republican foes.

But Obama said that the change he had wrought included ending the ban on gays serving openly in the military, regulatory reform in the finance industry, his health care law, and his decision to finally pull all US troops out Iraq.

"We've been able to decimate al-Qaeda and make sure that Osama bin Laden never again walks on the face of this earth -- that's change," he said.

Obama, who has seen his approval ratings decline to the low to mid 40 percent range amid high unemployment and lagging economic growth, faces a tough reelection fight next year.

He promised, if he wins a second term, to tackle comprehensive immigration reform -- the lack of which has dismayed the crucial Hispanic voting bloc and to forge an energy policy that deals with climate change.

"We've got more work to do," he said at the event where the cost of tickets started at $5000.

"Who are we? What do we believe in? What do we care about? What are the better angels of our nature that we want to make sure are reflected in our politics day in, day out?" he asked.

"Change is hard. Change takes time. But change is possible," he said, in a speech which coaxed supporters to his side, as distinct from the fiery shots at Republicans he took last week on a bus tour of North Carolina and Virginia.

The president is trying to piece together the coalition of voters, including the young, highly educated middle classes, African Americans and Hispanic voters who helped him claim the White House in 2008.

He is facing problems however in winning over white working class Americans in key swing states and crucial independents, so is even more reliant on a big turnout from core Democrats than he was in the last election.

Perhaps with an eye on the youth vote on Tuesday, the White House announced a plan to lower monthly payments for 1.5 million Americans burdened by student loans.

The move comes in the latest in a series of executive orders by Obama taking action on the economy under the banner "We Can't Wait" a reference to what the White House says is Republican obstruction to the president's jobs plan.