It’s the intramural D.C. squabble that blew up as quickly as an ocean rain squall: the Marco Rubio vs. Rand Paul Cuba Smackdown of 2014.

Why are two Republican senators, both probable presidential contenders, fighting over President Obama’s decision to reopen relations with communist Cuba? Like lots of things in official Washington, it’s complicated. There are both personal and political reasons for the fight.

One thing is sure: It’s bitter.

Kentucky Senator Paul doesn’t know what he’s talking about, says Senator Rubio.

Rubio is “an isolationist who wants to retreat to our borders and perhaps build a moat,” charges Paul.

Let’s start with Rubio’s side of things. The Florida lawmaker and son of Cuban immigrants has been the face of GOP opposition to Mr. Obama’s surprise Cuba move. He’s arguing that the United States will receive nothing for loosening travel restrictions and establishing other means of contact with Havana. The Castro regime will remain in place, its grip on power unaffected.

It’s an issue that Rubio obviously cares deeply about. It’s also historically very important to his state, where conservative Cuban-Americans have long been a powerful political bloc.

“I don’t care if the polls show that 99 percent of people believe we should normalize relations in Cuba. I’d still believe that before we can normalize relations in Cuba, democracy has to come first, or at least significant steps towards democracy,” Rubio said Wednesday.

Paul, for his part, is trying to carve out a niche as a Republican presidential contender with a different kind of foreign policy position. If there’s a word that sums it up, it’s “non-interventionist.” He’s been skeptical of the virtue of deploying US power overseas in the past.

So he came out – mildly – in favor of the president’s actions. He said in a radio interview earlier this week that Obama’s Cuba opening was “probably a good idea and that the 60-year-old US embargo on trading with Cuba hasn’t been effective.

“If the goal is regime change it sure doesn’t seem to be working,” Paul said.

This is where the fight began. Challenged from within his own party, Florida’s Rubio said Kentucky’s Paul “has no idea what he’s talking about.”

Paul bided his time then unleashed a stream of taunting tweets on Friday.

“Hey @marcorubio if the embargo doesn’t hurt Cuba why do you want to keep it?” he began.

Hey @marcorubio if the embargo doesn't hurt Cuba, why do you want to keep it? — Senator Rand Paul (@SenRandPaul) December 19, 2014

“Senator @marcorubio is acting like an isolationist who wants to retreat to our borders and perhaps build a moat. I reject this isolationism,” he continued.

Senator @marcorubio is acting like an isolationist who wants to retreat to our borders and perhaps build a moat. I reject this isolationism. — Senator Rand Paul (@SenRandPaul) December 19, 2014

And so on. He ended by asking Rubio why the US shouldn’t trade with Cuba, if it traded with China and Vietnam.

For Paul, what’s the advantage of pushing this quarrel? He gets to try to redefine his own image, while throwing mud on a possible rival.

He’s the one sometimes called an “isolationist.” Now he gets to use that label on somebody else while coming out in favor of economic engagement. How will that play in GOP primaries? That’s a huge and very interesting question that won’t be answered until Paul’s presidential campaign, if he tries one, gets underway.

Rubio’s tried to shut his rival down by belittling him. National security hawks have tried that in regards to Paul’s opposition to drones and National Security Agency surveillance. That hasn’t worked as well as they’d like.

Rubio, meanwhile, is defending an embargo that’s broadly seen as ineffective by the American people, if polls are any guide. In recent years, even the Florida Cuban-American community has become more supporting of lifting the embargo as the oldest refugees pass away and are replaced by younger escapees with family still on the island.

That doesn’t mean Rubio should cave, notes Bloomberg View political scientist Jonathan Bernstein. It’s a subject the Floridian obviously cares about. Political polarization may work in his favor: Many Republicans may reflexively oppose Obama’s move even if they think the embargo’s time is past, just because it’s Obama’s idea.

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That could help Rubio in the early winnowing process leading towards GOP primaries. If he wins the nomination, the issue might be forgotten by the time November 2016 rolls around.

“It doesn’t matter whether Obama’s policy is popular. It doesn’t even matter whether it’s successful. Strong opposition is almost certainly the right electoral play for Rubio,” writes Bernstein.