Washington (CNN) Barack Obama used his departing words as President Wednesday to offer an assured -- if not entirely optimistic -- outlook for a country governed by Donald Trump.

"At my core I think we're going to be OK," Obama said as he concluded his final news conference at the White House. "We just have to fight for it, work for it, and not take it for granted."

"I know that you will help us do that," he told reporters assembled in the White House briefing room.

If the message was still hopeful, it was a sharp downgrade from the grand visions of progressive change that propelled Obama to the presidency eight years ago.

In his question-and-answer session with reporters, Obama said that after two terms of political warfare with Republicans, he was emerging unbowed in his faith in the US and its citizens. But he continued to express concerns about his successor's stance on Russia and his readiness for office.

"I believe in this country. I believe in the American people. I believe that people are more good than bad," Obama said. "I believe tragic things happen. I think there's evil in the world, but I think at the end of the day, if we work hard and if we're true to those things in us that feel true and feel right, that the world gets a little better each time."

"That's what this presidency has tried to be about," he continued.

Conceding that Trump may not take his advice on issues, Obama said he would avoid weighing in on specific policy matters during his post-presidency, using his time instead to write and "not hear myself talk so darn much."

'Core values'

But he predicted he would voice concern if "core values" are being threatened.

"I put in that category if I saw systematic discrimination being ratified in some fashion. I put in that category explicit or functional obstacles to people being able to vote, to exercise their franchise," Obama said.

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Obama said he was calmed by the notion of the Oval Office as a moderating factor on Trump's bombastic tendencies.

He said once Trump gets into office and is hit with the intricate details of governing, his thinking might shift on issues such as Obamacare and jobs.

"Once he comes into office and he looks at the complexities of how to in fact provide healthcare for everybody, something he says he wants to do, or wants to make sure that he is encouraging job creation and wage growth in this country, that may lead him to some of the same conclusions that I arrived at once I got here," Obama said. "But I don't think we'll know until he has an actual chance to get sworn in and sit behind that desk."

In a news conference that will likely mark the final time Obama speaks in public before he departs the US Capitol on Friday as an ex-president, Obama described the phone calls between him and Trump as "constructive" and at times "lengthy."

He said the greatest advice he could give -- and has given -- to Trump, is to rely on others around him.

"This is a job of such magnitude that you can't do it by yourself," Obama said.

Obama opened the news conference rebuffing Trump, issuing a vocal defense of the White House press corps, insisting the reporters who covered his administration were an essential facet of a functioning democracy.

"We are accountable to the people who send us here. And you have done it," Obama said. "You're not supposed to be sycophants. You're supposed to be skeptics."

His remarks stood in direct contrast to the incoming president, who has lambasted news organizations reporting on his transition as reporting " fake news ." His choice to appear in the White House briefing room was also telling since Trump's team has floated the possibility of scrapping that venue for larger space.

Obama was continuing a tradition of taking reporters' questions for a final time before departing office. George W. Bush held his final news conference a week before leaving office, reflecting on some of the disappointments of his administration but also defending the controversial decisions he made over two terms in the White House.

Unlike Bush, Obama is leaving office with near-record approval ratings. A CNN/ORC poll released Wednesday showed 60% of Americans approve of the job he's doing as president.

Chelsea Manning

Obama's concluding news conference comes amid a flurry of last-minute activity, including handing down a commutation for national security leaker Chelsea Manning and a pardon for Gen. James Cartwright, convicted of lying to investigators in a leak probe.

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Obama defended the decision to commute Manning's sentence, saying that she served a "tough prison sentence." He said he looked at the particulars of the case the same way he had any other person whose sentence he had commuted.

"I felt that in light of all the circumstances, that commuting her sentence was entirely appropriate," Obama said from the briefing room.

He said the time she's already spent in jail would function as a deterrent for any future leakers while warning other potential whistleblowers to use established government channels to air grievances about the actions of the US government. But he said that "justice has been served" for Manning, a transgender woman who has been serving time at an all-male military prison in Kansas.

"The sentence that she received was very disproportionate relative to what other leakers had received," Obama said. "It made sense to commute and not pardon her sentence."

The decision has been lambasted by Republicans, who have accused Manning of being a traitor for disclosing hundreds of thousands of pages related to classified US programs.

Strained ties

Ties between the incoming and outgoing administrations have strained over Trump's relationship with Russia, which the US accuses of meddling in November's election. Trump has proposed friendlier ties to Moscow, which he said would lead to greater partnership on a series of sticky global issues from Syria to Ukraine.

Obama offered a cautious note on developing friendlier ties to Moscow, saying a constructive US-Russia relationship is "in America's interest and the world's interest."

But he said fostering warmer ties during his presidency was stymied by Russian President Vladimir Putin's combative stance when he returned to power in 2012.

Putin's "adversarial spirit" had "made the relationship more difficult," Obama said.