Though Republican candidates have been slow to formally enter the 2012 presidential race, the reaction to President Obama's budget speech Wednesday should leave no doubt the race for the White House is under way.

Several likely, but undeclared, GOP candidates were swift to condemn the president's plan. Obama vowed to cut $4 trillion from the deficit over 12 years, through a combination of spending cuts and tax hikes on high-income Americans.

"Today's speech was nothing more than window dressing," former Minnesota Gov. Tim Pawlenty said in a statement.

Former Massachusetts Gov. Mitt Romney, who just launched an exploratory committee and is positioning himself as the business-savvy alternative to Obama, went directly after the president's plan to raise taxes.

"President Obama's proposals are too little, too late. Instead of supporting spending cuts that lead to real deficit reduction and true reform of Medicare, Medicaid, and Social Security, the president dug deep into his liberal playbook for 'solutions' highlighted by higher taxes," Romney said.

Other potential candidates took to Twitter to express their outrage, mostly on taxes.

"President Obama doesn't get it: The fear of higher taxes tomorrow hurts job creation today," Mississippi Gov. Haley Barbour tweeted.

"Unbelievable -- President Obama blaming deficit on tax cuts! We do NOT have a revenue problem; we have a spending problem," wrote Gary Johnson, the former New Mexico governor who is expected to soon throw his hat in the ring.

Even the California Republican Party weighed in, accusing the president of trying to "tax our way out of deficit."

Obama made reference to the 2012 candidates in his address at George Washington University, noting that they were championing the GOP budget proposal outlined by Rep. Paul Ryan, R-Wis.

He challenged that proposal as unfair to seniors and the poor, and said he wanted to take a more balanced approach by rolling back the Bush tax cuts on those making above $250,000. He acknowledged the political difficulty in doing so.

"Without even looking at a poll, my finely honed political instincts tell me that almost nobody believes they should be paying higher taxes," Obama said.