President Barack Obama has some advice for Donald Trump: Whine less and campaign harder.

As the Republican presidential hopeful has fallen further behind in nationwide and swing-state polls, Trump has alleged that the general election is being “rigged” in favor of his opponent, Democratic nominee Hillary Clinton.

Obama, who has endorsed and campaigned for Clinton, shot back on Tuesday by calling the GOP standard-bearer’s comments baseless — and poor campaign tactics.

[White House to Trump: We Dare You to Take on FLOTUS]

“I’d advise Mr. Trump to stop whining and go make his case to get votes,” Obama said during a Rose Garden joint press conference Tuesday with Italian Prime Minister Matteo Renzi.

Obama said Trump is trying to discredit the election process and outcomes before all the votes have been cast, something he called “unprecedented” in American history.

Obama to Trump: ‘Stop Whining’

For decades, losing major-party candidates have telephoned the winners and pledged to find ways to work together. Obama signaled he is concerned Trump might have other plans for election night.

Losing candidates typically have recognized there is “something more important than an individual campaign,” Obama said. “Democracy, by definition, works by consent, not by force.”

Addressing Trump’s warnings about widespread voting fraud, Obama contended that “every expert” from all political affiliations have concluded that instances of large-scale fraud “are not to be found.”

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And despite some of the rhetoric Trump has lobbed at him — and he back at the billionaire — Obama vowed to welcome Trump, should he win, to the White House on Inauguration Day and escort him to the Capitol “for a peaceful transfer of power.”

Asked about Trump’s contentions that the president and Clinton talk too tough on Russia, Obama pointed to several areas on which his administration has worked with Moscow, but he also blamed that country’s “aggression” in places like Syria and Ukraine for the chilly relationship.

And he took Republican lawmakers to task for long holding “hawkish” stances on Russia before recently “echoing” Trump’s campaign-trail talk of bringing Moscow in as more of an ally.

Of those perceived GOP shifts, Obama said: “It’s quite a reversal.”

Contact Bennett at johnbennett@cqrollcall.com. Follow him on Twitter @BennettJohnT.