Oliver criticized Trump's portrayal of himself as a successful businessman while argued the Republican is thin-skinned, a liar and inconsistent with his public positions. 
More generally, he suggested it could be dangerous for Trump to be president and argued that people needed to speak out.
“At this point, Donald Trump is America’s back mole: it may have seemed harmless a year ago, but now that it’s gotten frighteningly bigger, it is no longer wise to ignore it,” said Oliver, who had pointedly refused to do a big piece about Trump on HBO's "Last Week Tonight."
“It’s time to stop thinking of the mascot and start thinking of the man, because a candidate for president needs a coherent set of policies. Whatever you think about Marco RubioMarco Antonio RubioWhite House staggers after tumultuous 48 hours Erdoğan got the best of Trump, experts warn Hillicon Valley: GOP lawmakers offer election security measure | FTC Dem worries government is 'captured' by Big Tech | Lawmakers condemn Apple over Hong Kong censorship MORE and Ted CruzRafael (Ted) Edward CruzHillicon Valley: GOP lawmakers offer election security measure | FTC Dem worries government is 'captured' by Big Tech | Lawmakers condemn Apple over Hong Kong censorship Lawmakers condemn Apple, Activision Blizzard over censorship of Hong Kong protesters The Hill's Morning Report — Trump's impeachment jeopardy deepens MORE, at least you basically know where they stand, but Trump’s opinions have been wildly inconsistent. He’s been pro-choice and pro-life, for and against assault weapon bans, in favor of both bringing in Syrian refugees and deporting them out of the country, and that inconsistency can be troubling.
Oliver noted that Trump is ahead in most of the states holding contests on Super Tuesday, which he said was a "big deal."
"We have mostly ignored Trump on this show, but he has now won three states, has been endorsed by Chris Christie and polls show him leading most Super Tuesday states, which is a big deal. Since 1988, every candidate who's won the most states on Super Tuesday went on to become their party's nominee."
He also called out Trump for what he said was a lie about being asked to appear on "Last Week Tonight."
"I think he just doesn't care about what the truth is," he said.
He then hit on Trump's claim that he's self-funding his campaign and targeted the front-runner for saying he's "tough."
"For a tough guy, he has incredibly thin skin," Oliver said.
Oliver added that Trump loves to threaten to sue people.
"I'll sue you is Trump's version of Bazinga. It doesn't really mean anything, but he says it all the time," he said.
"But perhaps Trump's biggest selling point as a candidate is success. And where could people get that idea," he said, before the show flashed to several clips of Trump talking about how successful he is.
But Oliver said Trump's claims were false. He referred to Trump as "Donald Drumpf," which he said would have been Trump's name before his family changed it.
"Stop and take a moment to imagine how you would feel if you just met a guy named Donald Drumpf, a litigious serial liar with a string of broken business ventures and the support of a former KKK leader who he can't decide whether or not to condemn."