President Barack Obama and Republican challenger Mitt Romney described contrasting visions for bolstering the middle class during the first presidential debate in Denver Wednesday night, sparring over health care and how to best manage a federal budget in a time of scarcity.

With Romney lagging behind the president in most polls going in, the debate was widely viewed as a crucial opportunity for the Republican to inject fresh momentum into his campaign. Romney largely delivered, marshaling concrete examples to fortify his points and often appearing more aggressive and nimble than Obama as the president waded into policy specifics.

Set against the backdrop of a sluggish economy, the debate focused on which candidate is better positioned to provide economic opportunity while taming a ballooning federal deficit. Discussions about tax policy consumed a conspicuous amount of time, while cultural issues like abortion and same-sex marriage were absent.

Continuing an argument that animated his reelection campaign, Obama called for a federal government that actively promotes prosperity. He tied Romney to the economic policies that precipitated the financial crisis of 2007.

“The question here tonight is not where we’ve been but where we’re going,” Obama said. “Governor Romney has a perspective that says if we cut taxes skewed toward the wealthy and roll back regulation we’ll be better off.”

Romney cast that approach as a mistaken belief that “a bigger government, spending more, taxing more, regulating more -- if you will, trickle-down government -- will work.” He said the president’s policies have bred uncertainty in the business world, held back job creation and led middle-class incomes to stagnate.

“There’s no question in my mind that if the president were reelected you’ll continue to see a middle-class squeeze, with incomes going down and prices going up,” the former Massachusetts governor said.

Romney said his program would encourage economic growth by lowering tax rates, a goal he said he would accomplish without raising the tax burden on the middle class or reducing the share that the wealthy pay in taxes. Calling the expanding budget deficit a “moral issue,” Romney introduced a test for where to cut spending: “Is the program so critical it is worth borrowing from China to pay for it?”

“The revenue I get is by more people working, getting higher pay, paying more taxes,” Romney said.

Obama sought to debunk Romney’s approach by saying it would be impossible to slash taxes and increase military spending -- Romney made a point of not cutting defense spending as he said Obama would – while keeping the deficit under control. The result, Obama said, would be “drastic cuts in things like education, making sure that we are continuing to invest in basic science and research, all the things that help America grow.”

By contrast, Obama said, his plan would call for Americans making more than $250,000 per year to be taxed at the higher rates that prevailed under President Bill Clinton, calling for an additional dollar in tax revenue for every $2.50 in spending reductions. That revenue, in addition to the savings flowing from the winding down of the wars in Iraq and Afghanistan, should be reinvested in education and developing new energy sources.

“The federal government has the capacity to help open up opportunity and create ladders of opportunity and create frameworks where people can succeed,” Obama said.

Health care consumed much of the debate, with Romney pledging to repeal Obama’s sweeping health care law and advocating a system in which private competition holds down costs. He said the Affordable Care Act imposes undue costs on businesses and on Americans who would be required to purchase health insurance.

“My experience is the private sector typically is able to provide a better service at a lower cost,” Romney said, adding later that “the right answer is not to have the federal government take over health care.”

Obama defended the Affordable Care Act -- and embraced the term Obamacare coined by his foes -- as a means of safeguarding the middle class against the potentially ruinous costs of illness, describing the previous approach as “leave a bunch of people uninsured and let them fend for themselves.” Gazing directly into the camera, the president defended his health care law -- something critics from his own party have accused him of failing to do vociferously enough -- by saying it controls costs and helps prevent insurance companies from denying people coverage.

“Insurance companies,” Obama said, “can’t jerk you around.”

Medicare also emerged as a prominent topic. Romney also reiterated his proposal, first lent prominence by running mate Paul Ryan, that would give future senior citizens a choice between enrolling in Medicare and receiving vouchers to purchase private insurance. He also criticized the Affordable Care Act’s attempt to curtail health care spending by appointing a board of experts to regulate Medicare reimbursements, saying the measure would cut $716 billion from Medicare.

“It puts in place an unelected board that tells people ultimately what treatments they can have. I don’t like that idea,” Romney said (as Obama later pointed out, the advisory board Romney mentioned is barred from rationing care or cutting benefits).

In response, Obama offered a criticism similar to his justification for the Affordable Care Act: that the guiding hand of government is necessary to curb the predations of the private sector. Under Romney’s plan, Obama said, a two-tiered system would emerge in which insurance companies cherry-picked healthier seniors and left Medicare to collapse under the weight of Americans who are more expensive to treat.

As a result, Obama said, the elderly would be “at the mercy of the private insurance system precisely at the time they’re most in need of private health care.”

In response to a question about the role of government regulation, Romney conceded that “regulation is essential” but said that under Obama “regulation has become excessive and it has hurt the economy.” Romney cited the Dodd-Frank financial reform bill, saying its vague rules on who is qualified for mortgage lending had made banks unwilling to lend.

But Obama noted that Romney has called for the law’s repeal and suggested that the Republican candidate did not have an alternate solution to safeguarding against another financial crisis.

“The question is, does anybody out there think that the big problem we had is that there was too much oversight and regulation of Wall Street?” Obama asked. “Because if you do, Governor Romney is your candidate.”