President Obama speaks about the Affordable Care Act at Miami Dade College on Oct. 20 in Miami. (Lynne Sladky/AP)

MIAMI GARDENS, Fla. — With presidential pre-election polls heavily favoring Democrat Hillary Clinton, President Obama aimed his attacks Thursday at Sen. Marco Rubio and other Republican officials who have supported GOP nominee Donald Trump, despite his controversial campaign and derogatory remarks about immigrants and women.

The president was appearing at Florida Memorial University, a historically black college and the kind of place where voters turned out for him in large numbers in 2008 and 2012. “There’s only one way we lose this election — if we don’t turn out,” Obama said. “We got to turn out big and not leave any doubt.”

Much of Obama’s speech was focused on questioning the honesty and ethics of Republican politicians who have condemned Trump but still back him. He was especially critical of Rubio (R-Fla.), who is in a tough battle for the state's Senate seat with Democrat Patrick Murphy.

“How can you call him a con artist and dangerous and object to all the controversial things he says and say I am still going to vote for him?” Obama asked of Rubio. “C’mon, man. You know what that is. It is the height of cynicism.”

He returned to the subject a few minutes later, noting that Rubio had said during the Republican primaries that Trump was unfit to handle the country’s nuclear codes and was a con man. “Why does Marco Rubio still plan to vote for Donald Trump? Why does he support Donald Trump?” Obama asked.

Obama also mocked Republicans who recently pulled their endorsements after The Washington Post revealed a video in which Trump can be heard boasting that he had groped women. The president insisted that such a late disavowal of the candidate was meaningless and accused Republicans of lacking standards. He said his political opponents had criticized him for not taking a tougher stand against Russian aggression, but gave Trump a pass for praising Russian President Vladimir Putin.

“Now all of a sudden you are okay with your nominee having a bromance” with Putin, Obama said.

Obama attacked Republicans for sticking with Trump when he made controversial remarks about Mexicans. “Where were you when your party's nominee called immigrants murderers and rapists?” he asked.

The Clinton campaign’s biggest worry is that young and minority voters will not turn out for Clinton in the same numbers that they have backed Obama.

“Trump can’t hear you from here,” Obama said when the crowd began to boo at the mention of the Republican nominee’s name. “But he can hear you when you go to the ballot box and vote.”

Obama briefly addressed Trump’s claims that the election is rigged and that he might not accept the results. On Thursday, Trump joked to cheers at a rally in Delaware, Ohio, that he would “totally accept the results of this great and historic presidential election — if I win.” Trump then said more seriously that he would accept a “clear” result, but reserved the right to challenge anything “questionable.”

Obama warned that the Republican’s words risked undermining the country’s institutions and overturning centuries of tradition. “That is not a joking matter. That is dangerous,” Obama said. “When you try to sew the seeds of doubt in people’s minds ... then you are doing the work of our adversaries.”