There's an obvious problem with this line of reasoning, however: Sweden doesn't have a president. As a constitutional monarchy, its head of government is its prime minister, currently Stefan Löfven. Its head of state would be its monarch, currently King Carl XVI Gustaf.
It's not just pedants who noticed Rubio's slip – Swedish royalists did, too.
“One would expect that these guys, who want to be the most important leader in the world, if they want that job, they should be able to know certain facts – for example that some European countries are monarchies,” Roger Lundgren, editor of Sweden’s Kungliga magazine and a leading commentator on Sweden's royal family, told the Local.
The royal expert went further in his criticism of Rubio – and by extension, other Americans. “The thing with some American politicians, such as Sarah Palin, is – I don’t want to use the word stupid, but I do. They are. They are so ignorant about the rest of the world,” he said. "They think there are two monarchies in the world. And that’s the U.K. and Monaco, because of Grace Kelly."
This isn't the first time it's been suggested that Rubio's knowledge of European constitutional monarchies is lacking. Earlier this year, Rubio said that Sanders would be a great president for Norway – another country with a monarch who serves as the head of state. He later explained that he had switched his comment to Sweden as he "got a little bit of heat from the Norwegians," Politico reports.
For reference, all three Scandinavian countries (Denmark, Norway and Sweden) are constitutional monarchies. If Rubio is looking for a president in northern Europe, he might want to try Finland (though the Finnish president must share his or her executive powers with the prime minister).