Trump and McConnell ate lunch with Vice President Mike Pence at the White House earlier in the day, but the press conference was not listed on his daily schedule.
Here are some of the key moments from the appearance:
Trump said his relationship with McConnell is "outstanding," denying reports since the summer of the two powerful Republicans' growing frustration with each other.
After first discussing his administration's current efforts at a tax overhaul, Trump suddenly pivoted to describe his rapport with McConnell.
"My relationship with this gentleman is outstanding [and] has been outstanding." Trump said.
McConnell later echoed Trump's sentiment and pushed back on the rumors of discord.
"I think what the president and I would both like to say to you today, contrary to what some of you may have reported, we are together totally on this agenda to move America forward," McConnell said.
Opioid national emergency, investigation into Rep. Marino
Trump said that next week, his administration plans to declare a national emergency to combat the opioid epidemic.
"We're going to be doing that next week," Trump said. "It's a very important step, and to get to that step, a lot of work has to be done, and it's time-consuming work."
Trump said he watched a special investigation by "60 Minutes" and The Washington Post that examined Congress' role in exacerbating the opioid crisis. The investigation pointed a finger at Rep. Tom Marino, R-Pa., as spearheading efforts to pass a bill that makes it harder for the Drug Enforcement Agency to halt suspicious shipments of drugs. Marino is the Trump administration's nominee to lead the Office of National Drug Control Policy. After viewing the report, Trump said he will be reconsidering the nomination.
"He was a very early supporter of mine from the great state of Pennsylvania," Trump said of Marino. "He's a great guy. I'll look at the report and take it very seriously because we will have a major announcement probably next week on the drug crisis and on the opioid massive problem, and I want to get that absolutely right."
"This country — and frankly, the world — has a drug problem," he added. "The world has a drug problem, and we have it, and we'll do something about it, and I'll have a major announcement on the drug problem next week. We'll be looking into Tom."
"I'd like to see it end," Trump said of the investigation. "The whole Russian thing was an excuse for the Democrats losing the election."
"There has been absolutely no collusion," Trump said. "It's been stated that they have no collusion. They ought to get to the end of it, because I think the American public is sick of it."
Niger ambush response
Almost two weeks after four Green Berets were killed in an attack in Niger, the Trump administration has faced criticism over its response. On Monday, Trump said he plans to call the families of the fallen soldiers to offer his condolences. But he also falsely claimed that Barack Obama and other presidents did not make personal calls to bereaved military families.
"The traditional way, if you look at President Obama and other presidents, most of them didn't make calls. Lot of them didn't make calls. I like to call when it's appropriate, when I think I'm able to do it. They have made the ultimate sacrifice. So generally I would say that I like to call," Trump said.
He said he plans to call and send letters to the families "either today or tomorrow."
When challenged by a reporter, Trump walked back his response.
"I was told that he didn't often. Lot of presidents don't," Trump said. "President Obama, I think, probably did sometimes. Maybe sometimes he didn't. I don't know. That's what I was told. All I can do is ask my generals. Other presidents did not call. They'd write letters. Some presidents didn't do anything. But I like the combination."
Former Obama advisers were quick to rebut Trump's claim.
Hillary Clinton and NFL protests
After tweeting Monday morning that he was recently asked if he thought Hillary Clinton would run for president again in 2020 and saying, "I hope so," Trump repeated the position when a reporter mentioned her in relation to the NFL national anthem protests.
"I hope Hillary runs. Hillary, please run again," he said.
Clinton has said that football players have the right to kneel during the national anthem in protest of racial injustice and that the action is "not against our anthem or our flag." Trump has repeatedly called attention to the protests and has said that the NFL should institute a rule requiring players to stand.
"I think she's wrong," Trump said. "It's that thinking — that is the reason she lost the election. When you go down and take a knee or any other way, you're sitting, essentially, for our great national anthem. You're disrespecting our flag and disrespecting our country."
"If Hillary Clinton actually made the statement that ... sitting down during the playing of our great national anthem is not disrespectful, then I fully understand why she didn't win," he continued. "There are a lot of reasons she didn't win, including the fact that she was not good at what she did."
Taking on health care and the pharmaceutical industry
Last week Trump made two major moves regarding the Affordable Care Act: He announced that he plans to discontinue making cost sharing reduction (CSR) payments, which help insurance companies pay for subsidies that benefit the poor, and he signed an executive order that will expand expand the availability of association health plans and limited-duration plans.
"Obamacare is a wreck. It's a mess and destroying lives," he said. "I want to get health care that's much more affordable and much better health care, and that's what we're doing."
Still, he said he and McConnell are working on a complete repeal and replacement of the ACA.
"We will come up in the early to mid-part of next year, and we will have a vote. We feel confident we have the votes, and we know what the plan is. I believe Republicans and Democrats are working together very hard right now to do an intermediate short-term plan because Obamacare is a disaster," said Trump.
He said he next plans to take on the pharmaceutical industry.
"We're going to get the costs way down," Trump said. "We are going to get drug prices and prescription drug crisis way down because the world is taking advantage of us. The world is taking advantage of us when this happens, so that will be very important."