Washington (CNN) -- Fresh off a three-primary sweep that bolstered the perception he is the inevitable Republican presidential nominee, Mitt Romney on Wednesday blasted President Barack Obama for running what he called a "hide-and-seek" campaign that lacked candor.
In remarks to a media convention that Obama addressed the day before, Romney responded to the president's harsh attacks on Republicans by accusing Obama of trying to divert attention from his own failed record through "straw men" arguments.
Citing Obama's recent comment to Russia's president, caught by a still-live microphone, that he could be more flexible after his re-election in November, Romney told the gathering of newspaper publishers and editors that the incident "calls his candor into serious question."
"He does not want to share his real plans before the election, either with the public or with the press," Romney said. "By flexibility, he means that 'what the American public doesn't know won't hurt him.' He is intent on hiding. You and I will have to do the seeking."
Romney also took aim at Obama's speech Tuesday, saying the president "railed against arguments no one is making -- and criticized policies no one is proposing." "It's one of his favorite strategies -- setting up straw men to distract from his record," Romney said, later adding: "With all the challenges the nation faces, this is not the time for President Obama's hide-and-seek campaign."
The competing speeches effectively launched the fall presidential campaign, pitting the Democratic president running on a populist theme of sticking up for the middle class against the Republican businessman and former Massachusetts governor proposing traditional GOP policies of smaller government, lower taxes and less regulation to drive economic growth.
"Almost every measure that the president has taken made it harder for small business to decide to grow in America or for big business to stay here," Romney said of Obama in response to questions after his speech. "I don't think that is what the president intended it to do but that is what it has done."
Overall, Romney said, "I don't think this has been a great presidency." While economic recovery has taken root after the 2008 recession, Romney scoffed that it only happened after "3½ years" and the expiration of government stimulus programs championed by Obama.
"Every recession ends and people get back to work," Romney said, repeating a line from the campaign trail that this recovery has been the slowest in U.S. history.
On Tuesday, Obama delivered what amounted to his strongest campaign speech so far and referred to Romney by name for the first time in an address.
In attacking a Republican budget plan passed by the U.S. House of Representatives, Obama said that "one of my potential opponents, Gov. Romney, has said that he hoped a similar version of this plan from last year would be introduced on day one of his presidency" and that Romney was "very supportive of this new budget."
To Obama, the Republican proposal prepared by House Budget Committee Chairman Paul Ryan of Wisconsin is a "Trojan horse" disguised as a deficit reduction plan that actually imposes a "radical vision" far to the right of the party's mainstream heroes such as Ronald Reagan.
"It is thinly veiled social Darwinism," Obama said. "It is antithetical to our entire history as a land of opportunity and upward mobility for everyone who's willing to work for it -- a place where prosperity doesn't trickle down from the top, but grows outward from the heart of the middle class."
He added that "by gutting the very things we need to grow an economy that's built to last -- education and training, research and development, infrastructure -- it's a prescription for decline."
The $3.5 trillion Ryan budget plan for 2013 would lower tax rates and cut spending while reforming the Medicare and Medicaid government-run health care programs for senior citizens, the disabled and the poor.
Ryan and other conservatives say major reforms are needed to subdue increasing federal deficits and debt, with particular focus on entitlement programs that are the main contributors to the budget imbalance.
For example, the Ryan budget would convert federal Medicaid funding for states into block grants. Such a step could increase the cost burden on states, but would give them more autonomy about how to set up their Medicaid programs. As a result, a state could reduce how many people are eligible or increase enrollees' cost-sharing obligations.
Obama blamed a polarized political climate for an inability to make progress on such key issues as deficit reduction and entitlement reform, arguing that the Republican shift to the right rejected moderate proposals acceptable to Democrats.
"The problem right now is not the technical means to solve it. The problem is our politics, and that's part of what this election and what this debate will need to be about," Obama said. "Are we, as a country, willing to get back to commonsense, balanced, fair solutions that encourage our long-term economic growth and stabilize our budget?"
He took particular aim at the Ryan budget proposal's tax reforms, spending cuts and entitlement reforms, which Obama said would shift the burden of deficit reduction to the middle class, senior citizens and the poor.
"In this country, broad-based prosperity has never trickled down from the success of a wealthy few," Obama said. "It has always come from the success of a strong and growing middle class."
Romney said Wednesday that Obama's criticisms were off-base, noting for example that the president's projected deep cuts to discretionary spending were based on an across-the-board approach that wouldn't apply.
He framed the election as a choice between bigger and costlier government that hinders growth and limits personal freedom, or letting free enterprise restore economic strength.
"If we become one of those societies that attack success, one outcome is certain -- there will be a lot less success," Romney said. "That's not who we are."
Romney's primary victories Tuesday in Wisconsin, Maryland and Washington, D.C., padded his wide lead in the delegate count over top challenger Rick Santorum and bolstered the sense that Romney has the nomination sewn up.
Conservative Sen. John McCain of Arizona said as much Wednesday, telling CNN's "Starting Point with Soledad O'Brien" that "whether Rick Santorum stays in or not is now basically irrelevant."
Ari Fleischer, a CNN contributor and former George W. Bush White House spokesman, said that Santorum earned the right to fight through Pennsylvania, but the race was all but over.
"I think the writing is on the wall. Does Rick Santorum want to read it is the question," he said.
Santorum said Wednesday that he intended to remain in the race. The former U.S. senator from Pennsylvania is pegging his hopes on a home state victory in the next set of primaries on April 24 to rebuild momentum for a campaign based on capturing conservative support by contrasting his principles and record against the more moderate Romney.
"We have to win here. And we plan on winning here," Santorum told reporters while campaigning in Pennsylvania, where polls show him holding a narrowing lead.
His campaign's communications director, Hogan Gidley, rejected a suggestion that Santorum would drop out if he fell behind in the polls in Pennsylvania, adding "this campaign is not poll-driven."
After Pennsylvania, several primaries in May take place in states with large numbers of Christian evangelicals who have supported Santorum elsewhere.
"May looks very, very good," Santorum said in reference to contests in Indiana, North Carolina, West Virginia, Nebraska and Texas.
"There's a move ... to make Texas a winner-take-all state," he added. "You throw those 154 delegates on our pile and all of a sudden, this race becomes a very different race."
According to CNN estimates, Romney has 654 delegates to 270 for Santorum, while fellow contenders Newt Gingrich and Texas Rep. Ron Paul trail well back. Romney's total is 57% of the 1,144 needed to clinch the nomination, and he would have to win 44% of the remaining delegates available to reach that threshold.
Obama, meanwhile, clinched the Democratic presidential nomination Tuesday with primary wins in Maryland, the District of Columbia and Wisconsin, CNN projected. Unlike the Republicans, Obama faced no serious opposition in his race, and his nomination was never in doubt.
CNN's John Helton, Joe Johns, Paul Steinhauser, Jason Hanna, Gabriella Schwarz, Phil Gast and Peter Hamby contributed to this report.