The event was held to support Republican Rick Saccone who is neck and neck with Democrat Conor Lamb in a congressional district that Trump won by over 20 points in the 2016 election. "If the Democrats were to prevail in western Pennsylvania, that would be quite an natural disaster", Rep. Charlie Dent said last week.
Mr Trump said on Saturday that Australia would be exempt from the tariffs.
Saccone, 60, is running against 33-year-old Democrat Conor Lamb on March 13 for a congressional seat that opened after Republican Rep. Tim Murphy, an avid pro-life lawmaker, resigned amid reports that he'd asked his mistress to get an abortion when he believed she was pregnant.
Donald Trump has called for drug dealers to face the death penalty in a bid to tackle the opioid epidemic ravaging the United States.
Trump derided Democratic Representative Maxine Waters as "a very low IQ individual" and said that Washington DC was full of "evil" people. "You ever see her?. We have to have him". You can't help it. "I may leave fast, or we may sit down and make the greatest deal for the world and for all of these countries, including, frankly, North Korea, and that's what I hope happens". He said if he runs again - which is "almost positive" - that he can't use his "Make America Great Again" tag line.
Trump occasionally mentioned Saccone, calling him "handsome" and insulting his opponent as "Lamb the sham".
Keep in mind the last person Trump offered a similar "endorsement speech" for was Republican Alabama Senate candidate Roy Moore.
Trump said that North Korea is hoping to make peace with the USA, and the time for that has come.
She also says the president "recognizes that manufacturing and steel belong in America and in Pennsylvania".
While praising Saccone - "this guy can really help me" - Trump spent more time attacking Lamb.
Foreign enemies, too, occupied Trump's mind. "Now, I never did polling on that - I don't know if that's popular, I don't know if that's unpopular". At the rally he said that seeking the death penalty for drug dealers "is a discussion we have to start thinking about. But that's OK. Because that's what we do, we handle things".
"I'm coming to you from Steel City", Saccone told FOX Business' David Asman. "We're gonna tax BMW". The Democrats - for the most part - can thank Trump for these wins.
"I don't know if you're ready".
The president lent his weight to Republican Rick Saccone in the final days of a surprisingly competitive special election outside Pittsburgh that could reverberate nationally ahead of the November midterm elections.
"This administration has already made unprecedented progress on behalf of the American people and I look forward to working with him to continue to deliver on the promises made", Saccone said in a statement following Trump's appearance.
"Do you think the drug dealers who kill thousands of people during their lifetime, do you think they care who's on a blue-ribbon committee?"
Speaking to a crowd of supporters in a packed airplane hangar outside of Pittsburgh, Trump gave one of his trademark speeches including a rare imitation where he feigned what it would be like to act "presidential".
THE FACTS: Exit polls found he got 41 percent of the votes from women in the election, not 52 percent.