President-elect Donald Trump arrives for his election night rally at the New York Hilton Midtown on Nov. 9, 2016. Reuters

In the final weeks of the turbulent 2016 election cycle, a 1993 letter from George H.W. Bush to Bill Clinton went viral online. Handwritten on the day of the Democrat's inauguration, Bush's message wished Clinton well and promised that he'd be "rooting hard" for the new president.

Years later, Donald Trump might not get the same warm reception from President Barack Obama.

Although Obama gave a heartfelt speech Wednesday urging Americans to keep their heads up and work together for a better nation, he's previously been outspoken about the Republican billionaire. As the United States moves forward under its new president-elect, remember what Obama has said he really thinks about Trump:

"He is, you know, the classic reality TV character ... He is a great publicity-seeker — and at a time when the Republican Party hasn't really figured out what it's for as opposed to what it's against." — Oct. 11, 2015

"Being president is a serious job ... It's not hosting a talk show or a reality show, it's not promotion, it's not marketing, it's hard. It's not a matter of pandering and doing whatever will get you in the news on a given day." — Feb. 16

"He has a long record that needs to be examined. And I think it’s important for us to take seriously the statements he’s made in the past." — May 6

"As a general rule, I don’t pay attention to Mr. Trump’s tweets." — May 6

"There’s no successful businessman in America who actually thinks the most successful businessman in the country is Donald Trump. I know those guys, and so do you, and I guarantee you, that’s not their view." — June 13

"What I think is scary is a president who doesn't know their stuff and doesn't seem to have an interest in learning what they don't know." — July 28

"America is already great, America is already strong. And I promise you, our strength, our greatness, does not depend on Donald Trump." — July 28

"Donald Trump calls it 'a divided crime scene' that only he can fix. It doesn’t matter to him that illegal immigration and the crime rate are as low as they’ve been in decades because he’s not actually offering any real solutions to those issues. He’s just offering slogans, and he’s offering fear." — July 28

"I think the Republican nominee is unfit to serve as president ... The notion that he would attack a Gold Star family that made such extraordinary sacrifices on behalf of our country, the fact that he doesn’t appear to have basic knowledge around critical issues in Europe, in the Middle East, in Asia, means that he is woefully unprepared to do this job." — Aug. 2

"I think I was right — and Mitt Romney and John McCain were wrong — on certain policy issues, but I never thought that they couldn't do the job." — Aug. 2

"If you supported me in '08, if you supported me in '12, if you think that I've done a good job, if you believe that Michelle has done a good job — everything that we've done over the last eight years will be reversed with a Trump presidency." — Friday

"Imagine if, when I was running, I had said one-tenth of the things that Donald Trump has said. People would immediately say, 'That person is not fit to be president.' It's not just with respect towards his attitude towards minorities — it's his lack of respect for the Constitution." — Friday

"I would feel deeply frustrated [about welcoming Trump to the White House] not because of anything he’s said about me, but because I would fear for the future of our country." — Friday

"Now, you may have heard that — this was just announced, I just read it, so I can’t confirm it’s true, but — this campaign has taken away his Twitter. In the last two days, they had so little confidence in his self-control, they said ‘We’re just gonna take away your Twitter.’ Now, if somebody can’t handle a Twitter account, they can’t handle the nuclear codes. If somebody starts tweeting at 3 in the morning because SNL made fun of you, you can’t handle the nuclear codes." — Sunday