US President Barack Obama waves before he speaks to students and parents about the rising costs of education at Washington-Lee High School in Arlington, Virginia May 4, 2012. [Photo/Agencies]

WASHINGTON - With his wife at his side and Air Force One as a campaign plane, President Barack Obama holds his first political rallies of the 2012 presidential race on Saturday, targeting two swing states that could be critical to his bid to retain the White House.

Obama, a Democrat, formally launched his Chicago-based re-election effort last year, but his official political events have been confined to fundraisers since then.

That changes this weekend.

The president, who was propelled to power in the 2008 election thanks in part to huge rallies across the nation, hopes to regain that momentum with events in large arenas in Columbus, Ohio and Richmond, Virginia. Thousands of people are expected to attend.

Since Republican Mitt Romney became his party's presumptive nominee, Obama has criticized his opponent in formal and informal situations - a sign that he is more than ready to start the attacks that are expected to characterize a potentially ugly and negative campaign. He is likely to be sharply critical of Romney during his Saturday rallies.

Republicans accuse Obama of infusing politics into his official White House events and scoff at the notion that his campaigning is just starting. The president has done official trips in recent months to highlight his energy record and to tout proposals to reduce costs for students. Young people are an important constituency for his campaign.

"We're ready to go," campaign manager Jim Messina told reporters in a recent conference call.  

"While Mitt Romney has been busy endearing himself to the Tea Party and making promises he can't keep, we've been busy building the largest grassroots campaign in modern American history."