WASHINGTON -- Barack Obama stepped behind the White House podium for the last time Wednesday, fielding questions from journalists crammed in for the occasion and offering assurances to Americans watching on TV.

But at times, his answers seemed aimed at an audience of one: The man who will replace him at noon Friday.

Obama gently chided Donald Trump's suggestion the U.S. might end its sanctions on Russia over Ukraine in exchange for nuclear stockpile reductions, saying it was in America's interest to ensure "we don't confuse why these sanctions have been imposed with a whole set of other issues."

And, with Trump vowing to move the U.S. Embassy in Israel to Jerusalem, a move that could further inflame tensions in the Middle East, Obama warned when "sudden unilateral moves" are made in the region, the results can be explosive.

Obama also defended his decision to cut nearly three decades off convicted leaker Chelsea Manning's prison term, a move Trump's team criticized. Obama said the former Army intelligence analyst had served a "tough prison sentence" already.

With no elections left to win or legislative battles to fight, Obama used his parting words to deliver one set of messages to his successor, a man who is his opposite temperamentally and politically.

Obama said he expected a new president, particularly one from the opposing party, to "test old assumptions," but he suggested it would be important for the next administration to "understand that there are going to be consequences, and actions typically create reactions."

The fact Obama was holding the afternoon news conference in the White House briefing room served as a symbolic counter to Trump.

The president-elect's aides have raised the prospect of moving daily news briefings out of their traditional West Wing home, sparking fears of attempts to push reporters out of the White House.

Obama addressed that worry: "Having you in this building has made this place work better," he said.

"You're not supposed to be sycophants; you're supposed to be skeptics," Obama said to reporters. "You're not supposed to be complimentary, but you're supposed to cast a critical eye on folks who hold enormous power and make sure that we are accountable to the people who sent us here."

Obama was taking a page out of the playbook used by Trump advisers, who often try to communicate with their boss on the airwaves.

The president's news conference earned him prime real estate on the networks Trump keeps on his office television throughout the day, with most cable news outlets carrying the entire hourlong event live.

For years, Trump's only presence in Obama's orbit was as an irritant and the chief promoter of the lie that the president was born outside the United States. When Trump challenged for the presidency, Obama worked to stop him and seemed all but certain that Americans wouldn't back the Republican's brash and divisive politics.

Since Trump's unexpected victory, Obama has largely set aside that history and sought to help ease his successor's transition into office. He's spoken with Trump by phone numerous times, sometimes at length, he said Wednesday.

Divulging some of his advice to the incoming president, Obama said he's told Trump, "This is a job of such magnitude that you can't do it by yourself."

Trump was ridiculed by Democrats for saying during his Republican convention speech that "I alone" can fix the problems ailing the nation.

After eight years in office, the president suggested he's eager to step away from the political spotlight for a time. "I want to be quiet a little bit and not hear myself talk so darn much," he said Wednesday. But he also served notice that as an ex-president, he would speak out if Trump violates America's "core values."

For all his campaign warnings about the dire implications of a Trump presidency and the threat the 45th president poses to his own policy achievements, Obama insisted he was at ease, even optimistic, upon stepping aside.

"At my core, I think we're going to be OK," he said.