Republican tax cuts will help you “lose a few extra pounds,” even “improve your love life,” President Obama chided on Friday.

When it comes to Mitt Romney’s budget plan, “they did not take their arithmetic course,” the president joked at a rally in Palm Beach, Fla., on Sunday. “They need to stay after school. They need to get some extra study hall in there. No recess for you.”

For his part, Romney counters that God isn’t going anywhere — certainly not out of his party’s platform or his own heart. His running mate, Rep. Paul Ryan (Wis.), says Obama’s iconic 2008 “Hope” posters have frayed and faded along with the economy.

On tax cuts and defense spending, religious piety and Medicare, Obama and Romney have unveiled fresh zingers and put-downs after the Republican and Democratic conventions.

The quips are pithy and memorable. Some are designed to capi­tal­ize on popular applause lines, others to amend for things not said. But their subtext reveals the serious business of trying to convince voters that they cannot trust what the other guy is peddling at a moment when many voters are starting to pay closer attention.

The president’s ribs against Romney’s tax plan aim to build on the theme that the former businessman is a rich elitist protecting the self-interest of the upper class by also making him appear reckless — willing to support tax cuts even as the national debt soars. Obama came up with the extended riff, campaign aides said, to push the idea that the GOP has few new ideas to jump-start the economy, even as they attack him along the same lines.

“Tax cuts when times are good. Tax cuts when times are bad. Tax cuts to help you lose a few extra pounds,” Obama said in Portsmouth, N.H., on Friday. “Tax cuts to improve your love life.”

He added that he does not think “another round of tax breaks for millionaires is what’s going to bring good jobs back to our shores, or pay down our deficit. We have been there. We’ve tried what they’re selling. It didn’t work then; it’s not going to work now.”

References to God

Romney’s references to God aim to accentuate his rivals’ most embarrassing convention moment: When Obama, arriving at the convention last week, reportedly demanded that Democrats reinsert a mention of God in the party platform — and even then it took the delegates three messy voice votes to do so.

“I will not take God out of . . . our platform,” Romney said in Virginia Beach. “I will not take ‘God’ off our coins, and I will not take God out of my heart.”

The attack also helps Republicans in their ongoing bid to portray their rivals as lacking faith in anything — private enterprise, a higher power — except big government to solve problems.

Democrats were “against God before they were for Him,” Ryan quipped during a rally in Colorado Springs.

Romney has sought to bolster his standing among the military, after he failed to mention U.S. troops in Afghanistan during his nomination acceptance speech in Tampa. In recent days, Romney has heavily criticized Obama for supporting a potential $100 billion in mandatory defense cuts as part of a bipartisan agreement to raise the nation’s debt ceiling last week.

Not that Obama and his surrogates are backing down on foreign policy. At the Democratic convention, Sen. John F. Kerry (D-Mass.) ripped Romney’s Afghanistan policy as inconsistent, saying he has at times favored removing U.S. troops before more recently arguing to keep the forces there past Obama’s 2014 deadline.

Obama has built on that criticism. “He won’t tell us how he’ll end the war in Afghanistan, in fact, didn’t even mention it in his speech at his convention,” the president said in Kissimmee, Fla., on Saturday.

Surrogates pile on

Other surrogates have piled on. Former president Bill Clinton, during his convention address, contended that Romney’s budget plan “doesn’t add up” because the former Massachusetts governor has not detailed which tax loopholes he would eliminate to make up revenue for the tax cuts he favors for the wealthy.

Obama picked up on the line Sunday in Palm Beach, Fla., after Romney avoided laying out specifics during an interview on “Meet the Press.”

“You add $5 trillion of new tax cuts, $2 trillion in new defense spending, and somehow you’re going to close the deficit without raising taxes on middle-class families?” Obama said of Romney’s plan.

On the flip side, Romney and Ryan have gotten help from Newt Gingrich, who during a CNN appearance on Sunday repeated the line Ryan used to mock Obama’s “Hope” poster as Republicans seek to portray Obama as failing to live up to his hype.

“Ryan’s line about the young person sitting in their bedroom looking out at the graying poster of Obama as it faded away sort of captured it,” Gingrich said.

The president has been just as aggressive in turning his rivals’ words around on them. During a Labor Day speech in Toledo, Obama parodied Romney for suggesting that the United States needs a “new coach” with a new “economic game plan.”

Obama told the crowd it was “time to punt” Romney’s budget plan and warned that his rival will throw a desperation “Hail Mary” pass by turning Medicare into a privatized voucher system.

“You don’t need that coach,” Obama said. “That’s a losing season.”