President Obama belittled congressional Republicans for taking vacations amid difficult deficit-reduction talks. He contrasted lawmakers with his young daughters. And he brushed off criticism of his Libya policy as a “fuss” that is all about politics.

Using the grand backdrop of an East Room news conference, Obama clearly had a mission Wednesday: to reassert a commanding presence on the economic and foreign policy issues that are defining his presidency — and could determine whether he wins reelection.

Wednesday’s appearance offered Obama a chance to regain the upper political hand that he has lost in recent weeks as gasoline prices rise, employment numbers continue to disappoint and a deficit-reduction deal with the GOP that would raise the country’s debt limit remains elusive.

He accused Republicans — no less than six times — of favoring corporate-jet owners over average folks in the party’s refusal to consider tax increases as part of a deficit deal.

And, showing a combative side that Americans rarely see, he said that Republicans “need to do their job.”

“They’re in one week, they’re out one week,” the president said. “And then they’re saying, ‘Obama has got to step in.’

“You need to be here,” he added sternly. “I’ve been here. I’ve been doing Afghanistan and bin Laden and the Greek crisis. You stay here. Let’s get it done.”

Republicans fired back quickly Wednesday, accusing Obama of shrinking from his responsibilities and trying to pressure them to raise taxes. While the president answered media questions, Senate GOP leaders scheduled a competing news conference to focus attention on their support for amending the Constitution to require a balanced federal budget.

House Speaker John A. Boehner (R-Ohio), who must satisfy the fervently anti-tax tea party wing of his caucus, said later that Obama’s remarks “ignore legislative and economic reality.”

“Republicans have been leading and offering solutions to put the brakes on this spending binge,” he said. “The president has been AWOL from that debate.”

Recent polls show that any bounce Obama experienced after the May 1 killing of Osama bin Laden and earlier signs of economic recovery has evaporated — and Republicans seeking to challenge the president in next year’s election have taken to calling him a failed leader. A Washington Post-ABC News poll from early June showed that nearly six in 10 Americans disapproved of his handling of the economy.

Recent economic setbacks have put pressure on the president to show that he is as focused on creating jobs as he is on cutting government spending. He has been traveling the country each week — visiting politically important states, including Pennsylvania and Iowa in the past week — to urge job creation and technology investments that could bolster U.S. manufacturing.

In fact, Obama began Wednesday’s news conference by imploring Congress to take new action to stimulate the economy. He called on Congress to extend a payroll tax cut, make loans to build new roads, reform patents and advance trade deals.

Throughout the news conference, he spoke with more vigor and specificity than he has at any point before about the potential dangers Americans will face if Republicans don’t agree by a “hard deadline” of Aug. 2 to lift the debt ceiling. He suggested that the GOP would be blamed for damaging cuts to the National Weather Service, food inspections, veterans benefits and Social Security payments.

“I’ve said to some of the Republican leaders, ‘You go talk to your constituents, the Republican constituents, and ask them are they willing to compromise their kids’ safety so that some corporate-jet owner continues to get a tax break,’ ” the president said. “And I’m pretty sure what the answer would be.”

Obama’s confrontational style extended to foreign policy matters as well.

He rejected the premise of a question on the constitutionality of the 1973 War Powers Resolution, passed by Congress to restrain presidential war-making after the undeclared Korean and Vietnam wars. Critics in both parties have charged in recent weeks that the U.S. role in trying to oust Libyan leader Moammar Gaddafi violates the resolution.

“I’m not a Supreme Court justice, so I’m not . . . putting my constitutional law professor hat on here,” he said.

Instead, as he did for much of the news conference, Obama turned the Libya question into a chance to portray himself as a good-faith actor operating in a sea of mal-intentioned politicians.

He accused critics of making a “cause celebre” out of protecting Gaddafi, who has killed Americans. Obama said that his administration has sent “reams of information” to Congress on the Libya effort, and that the United States has carried out its narrow mission there with success.

“So a lot of this fuss is politics,” he added.

Obama was most animated on the deficit debate, again taking pains to present himself as the one willing to make politically costly decisions about spending cuts.

He described himself as the commander in chief who has “difficult conversations with the Pentagon, saying, ‘You know what, there’s fat here [and] we’re going to have to trim it out.’ ”

The president’s stern new tone suggested that administration officials think the cordial outreach and behind-the-scenes negotiations they have been using in deficit-reduction talks with Republicans have not been working.

The White House had declined to discuss the details of negotiations, being led by Vice President Biden, until Friday, when Republicans walked out because of tax policy disagreements.

Among the changes the White House sought were rollbacks of tax breaks for corporate jets and hedge-fund managers — a small amount relative to the overall deficit but highly symbolic as the president tries to gain ground in the tax debate by painting the GOP as the party of the very rich.

Then, as if his earlier scoldings weren’t enough, Obama suggested that his daughters, Malia and Sasha, displayed a better work ethic toward their school assignments than the GOP has toward the debt ceiling.

“They’re not pulling all-nighters,” he said. “They’re 13 and 10. Congress can do the same thing. If you know you’ve got to do something, just do it.”