President Barack Obama called out Donald Trump for threatening not to accept November’s election results, saying Trump didn’t have what it takes to be president if he isn’t willing to abide by democratic tradition.

“We’ve got to do it big. We’ve got to leave no doubt,” Obama told a rowdy crowd in Miami Gardens, Florida on Thursday. “Because you notice the Donald is already whining that the vote’s going to be rigged before the game’s even over.”

Obama brought up Trump’s statement at a rally earlier Thursday that he would accept the election results “if I win,” countering, “There is no way to rig an election in a country this big.”

“I don’t know if Donald Trump has ever been to an actual polling place where you have Democrats and Republicans who are in charge of taking the votes,” Obama wondered. “But, you know, he doesn’t even worry if what he says is true. This is just about him worried that he’s losing.”

“Which means he really doesn’t have what it takes to hold this job, because I will tell you, there is a lot of time in this job where things don’t go your way,” he said.

“That is not a joking manner,” Obama said. “That is dangerous.”

Obama referenced a gaggle of Republican lawmakers condemning Trump’s talk of a “rigged” election—Sen. Marco Rubio (R-FL) said at a debate Monday that “I promise you there is not a 67-county conspiracy to rig this election” in Florida—and then wondered aloud why those politicians still say they would vote for Trump.

“You got Republican governors in battleground states like Ohio and North Carolina and Georgia and Nevada and Iowa and Texas and Arizona. Are they all in on this rigging? They’re not going to rig the election for Hillary Clinton,” he said, echoing a point Rubio made Monday.

“Even Marco Rubio says there is no rigging of the vote, which I’d like to give him credit for, except he’s refuting the dangerous, unprecedented claims of a candidate he says he’s still going to vote for! Which just gives you one more bit of proof that Marco seems to just care about hanging onto his job,” Obama said.