WASHINGTON - President Barack Obama is shifting from consoler to comic for his appearance before a mix of politicians, celebrities and journalists at Washington's premier black-tie dinner.

And some of his most prominent would-be rivals are in attendance, including Donald Trump.

The billionaire businessman was among those who arrived Saturday for the White House Correspondents' Association annual dinner, after a week when he challenged the president on conspiracy theories about his birthplace and the White House released Obama's detailed Hawaii birth certificate.

Watch: History of laughs at White House Correspondents Dinner

Newt Gingrich, another considering a presidential run in 2012, also was among the guests. Virginia Gov. Bob McDonnell and Obama confidant and Chicago Mayor-elect Rahm Emanuel were among those milling in the foyer with figures from the entertainment world such as actors Sean Penn and Scarlett Johansson.

Some 3,000 people are expected to attend.

Obama arrived later Saturday, a day after traveling to Alabama to meet with residents affected by the deadliest tornado outbreak in 40 years. 

But in a town consumed by politics and partisanship, the dinner is typically a light-hearted affair and an opportunity for the president to show off his humorous side. Obama has used his past appearances to crack jokes at everything from the infamous couple that crashed his first state dinner to the off-the-cuff speaking style of his vice president, Joe Biden.

The association was formed in 1914 as a liaison between the press and the president. Every president since Calvin Coolidge has attended the dinner.

"Saturday Night Live" comedian Seth Myers was booked to provide laughs at the dinner.

Some of the proceeds from the dinner pay for journalism scholarships for college students.

Several journalists will also be honored at the dinner: 

Dan Balz of The Washington Post and Jake Tapper of ABC News, for winning the Merriman Smith Award for presidential coverage under deadline pressure. Balz won for coverage of an unexpected appearance by Obama and former President Bill Clinton at a White House briefing, and Tapper won for revealing that Obama would ask Director of National Intelligence Dennis Blair to resign.

Peter Baker of The New York Times, for winning the Aldo Beckman award for sustained excellence in White House coverage, for stories dubbed "the education of a president." 

Michael Berens of The Seattle Times, for winning the Edgar A. Poe Award for excellence in coverage of news of national or regional significance. Berens uncovered flaws in a health care plan for seniors that resulted in neglect, abuse and even death.