SAN FRANCISCO >> President Barack Obama told supporters on Thursday he is pressing ahead with his agenda in a difficult political environment in Washington and that "change turned out to be a lot tougher than expected"

Obama addressed about 200 people who paid up to $35,800 apiece for the fundraiser at a San Francisco hotel, the first of four fundraisers of the day.

Even though he’s running for re-election from the White House, Obama said he still wants to mount a grassroots campaign. "We need you now more than ever," he said. "Your engagement, your involvement, your commitments are going to be critically important."

Political tensions have increased lately, with a near government shutdown earlier this month, a showdown looming on raising the nation’s borrowing powers and the ongoing debate over long-term deficit reduction.

Obama has called on Republicans and Democrats to work together. But Republicans, egged on by tea party activists, are demanding more spending cuts than Obama has proposed and are resisting his call for raising taxes on the wealthy. And, as Obama eases into his 2012-relection campaign, many of his liberal backers are pressing the president against making further concessions to the GOP on spending cuts and taxes.

Obama was interrupted by a small group among the paying guests who protested the detention of Bradley Manning, an Army private accused of leaking secret documents to Wikileaks.

"We paid our dues, where’s our change?" the protesters sang to the president.

"We’ll vote for you in 2012, yes that’s true. Look at the Republicans — what else can we do?"

Obama paused while security removed some of the protesters, then joked, "that’s a nice song. You guys have much better voices than I do."

Manning is suspected of illegally passing U.S. government secrets to the WikiLeaks website while serving as an Army intelligence analyst in Iraq. He was transferred this week to an Army prison in Kansas from the Marine brig in Quantico, Va., where he has spent the last nine months. He faces nearly two dozen charges, including aiding the enemy, a crime that can bring the death penalty or life in prison.

Obama earlier told supporters he understands their frustration over the compromises he’s made with Republicans, while preparing them for more to come.

During a raucous fundraiser focused on young people in San Francisco Wednesday night, Obama said his supporters are not alone in their frustration with progress in the nation’s capital.

"There are times when I’ve felt the same way you do. It’s a big, complicated, messy democracy," he said. "We knew this wouldn’t be easy."

Obama’s three-day West Coast swing — his most extensive travel since announcing his re-election bid — offered a glimpse of how Obama will seek to re-energize the independents and first-time voters who carried him to victory in 2008. Obama argues that more work must be done to make the vision of America he promised a reality, and that he is the only one who can see those hopes through.

"It is going to take more than a couple of years," Obama said. "It’s going to take us more than one term to finish everything that we need to do."

Obama senior adviser David Plouffe told the hundreds of young supporters gathered for the nighttime rally: "This is going to be a close campaign…The one thing we better assume is that it’s going to be closer than the last one."

In addition to the San Francisco fundraiser, Obama had three more planned for Thursday in Los Angeles. In between, Obama will squeeze in a town hall meeting in Reno, Nev., aimed at selling his deficit-cutting plan to a wary public.

"The deficit is real, our debt is real. We’ve got to do something about it. But how we do it is going to make a huge difference," Obama said during a smaller, high-dollar fundraiser Wednesday night.

The president and Republicans have both offered plans for bringing down the deficit, but vast differences exist over how to do so. The president is calling for $4 trillion in deficit reduction over 12 years, through a combination of spending cuts and tax hikes on the wealthy, while House Republicans have passed a plan that would reduce the deficit by nearly $6 trillion in a decade, in part by overhauling Medicare and Medicaid.

The president and Republicans have accused each other of pitching "radical" plans.

"I think it’s fair to say that their vision is radical," Obama told a town hall gathering Wednesday at the headquarters of Facebook, the huge social network company.

Brendan Buck, a spokesman for House Speaker John Boehner, returned fire. "What’s radical is piling up $9 trillion more in debt on the backs of our kids and grandkids," he said, echoing a GOP criticism that Obama’s plan would accomplish too little.

Obama’s mixing of politics and policy on this West Coast swing is a harbinger of things to come as he balances campaigning with the duties of the presidency.