Rounding out his two-day fundraising swing in California Thursday, President Obama told donors that passing new gun measures will be a "tougher" process than achieving immigration reform.

"I am very optimistic that we get immigration reform done in the next few months. And the reason I'm optimistic is because people spoke out through the ballot box, and that's breaking gridlock," Obama told about 30 donors gathered at a fundraiser in Atherton, Calif., Thursday. "It's going to be tougher to get better gun legislation to reduce gun violence through the Senate and the House that so many of us, I think, want to see - particularly after the tragedy in Newtown. But I still think it can get done if people are activated and involved."

READ MORE: Washington Has 'Cold Feet' on Gun Control, Says Obama Adviser

The bi-partisan "Gang of Eight" senators are expected to release an immigration plan when the Senate returns from its holiday recess next week, but the fate of gun measures is unclear as many Republicans and some moderate Democrats quibble with the universal background check requirement in the comprehensive gun package.

The president is making major speeches on gun control in states reeling from mass shootings in an attempt to drum up political support as the Senate considers gun legislation later this month.

"Part of the reason it's so hard to get this done is because both sides of the debate sometimes don't listen to each other," Obama said Wednesday in Denver, just miles from the site of a mass shooting at an Aurora, Colo., movie theater. "The people who take absolute positions on these issues on both sides sometimes aren't willing to concede even an inch of ground."

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"The only way this time will be different is if the American people demand that this time it must be different; that this time we must do something to protect our communities and our kids," he said.

On Monday, the president will speak about measures to reduce gun violence in Connecticut, where 20 children and six educators were gunned down at Sandy Hook Elementary School four months ago. Family members of those killed in the massacre in Newtown, Conn., are being invited to attend.

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President Obama's comments came at a brunch fundraiser at the home of Liz Simons and Mark Heising, director of a San Francisco investment firm and a board member at the Environmental Defense Fund. The president attended a second fundraising lunch for about 250 people at the home of John D. Goldman, a philanthropist and Levi Strauss heir, and his wife, Marcia Goldman, in Atherton, Calif. Tickets for the two events ranged from $1,000 to $32,400, and both fundraisers benefited the Democratic National Committee. President Obama was on a two-day fundraising swing through California that started on Wednesday.