Watch Mitt Romney's joke about Obama: Funny and effective?

Barack Obama walks into a bank.

So begins a zinger Mitt Romney let loose Sunday while campaigning for GOP Iowa Senate candidate Joni Ernst, who is locked in a tight race with Democratic U.S. Rep. Bruce Braley. The two are competing for the seat held by retiring five-term Democratic Sen. Tom Harkin.

"They say if you're running for office you shouldn't tell jokes. But I'm not running for office,” Romney told the crowd in Iowa. 

And thank goodness. Mitt the civilian is a lot funnier than Mitt the candidate. 

Need proof? Here’s his joke, in full:

President Obama went to the bank to cash a check and he didn't have his ID. And the teller said, 'You've got to prove who you are.'

He said, 'How should I do that?' She said, 'the other day Phil Mickelson came in, he didn't have his ID but he set up a little cup on the ground, took a golf ball, putted it right into that cup so they knew it was Phil Mickelson. We cashed his check.

And then Andre Agassi came in. And Andre Agassi didn't have his ID either. He put a little target on the wall, took a tennis ball and racquet — hit it onto that target time and again. We knew that was Andre Agassi so we cashed his check.

And she said to him, 'Is there anything you can do to prove who you are?' And [Obama] said, 'I don't have a clue.'

And she said, 'Well, Mr. President, do you want your money in small bills or large bills?'

If the joke is any indication, the two-time presidential candidate has loosened up considerably since his campaign days when he was often described as “robotic” and “uptight.” 

“Mitt Romney looks like a guy modeling briefs on a package of underwear,” David Letterman joked on CBS’s "Late Show with David Letterman" in 2012. “He looks like a guy who goes to the restroom when the check comes...He looks like a guy who would run a seminar on condo flipping ... He looks like that guy on the golf course in the Levitra commercial.”

That reputation, of course, made the former Mass. Governor an easy target for many comics during the last election season, when he was the frequent butt, rather than source, of some funny jokes.

Like this zinger from Letterman circa 2012. “They say that Paul Ryan will humanize Romney. And I thought, hell, an amoeba could humanize Romney.”

And while Obama was the butt of Romney’s joke Sunday in Iowa, it turns out Romney himself has been comic gold.

Romney jokes on late-night TV outpaced Obama jokes 2-1 during the last election cycle, according to a George Mason study, as reported by the Daily Beast. It turns out it’s a lot easier to make fun of a straight-laced, beer-snubbing Mormon with offshore accounts and a stunning tax rate than the nation's first black president. And, as the article notes, most comedians share the same political perspective as Obama. 

But that doesn't make the president completely immune from Letterman pokes. Take this one from October 2013:

"Obama said they've had some glitches with the Affordable Care website. I'll tell you something. If you order a pair of pants online and they send you the wrong color, that's a glitch. This is like a Carnival cruise, for God's sake! Today Obama was in so much trouble he called Hillary Clinton and he said, 'Could you start early?'" 

Joking aside, might Romney’s Obama joke hurt the President, or help the Republican candidate, Joni Ernst, who’s locked in the closest Senate race in the nation where no incumbent is running, according to public opinion polls? 

In fact, it might.

“When jokes are made – particularly about a political figure, or a party, or a process, or an institution – people’s perceptions or opinions of the target of the joke go down,” Jody Baumgartner, a political science professor at East Carolina University who studies the impact of political humor, told the Daily Beast. “So it does matter. It absolutely matters.”

In other words, the next time Obama walks into a bank, he’d better have his ID with him. 

And that’s no joke.