US President Donald Trump went to Pittsburgh in Pennsylvania to promote his steel and aluminium tariffs and back a Republican locked in a tight congressional race, but the US President didn’t stop there.

In a free-wheeling return to the bellicose rhetoric and tossed-off insults that characterised his 2016 campaign for the White House, Trump took shots at Oprah Winfrey while also branding a leading US media commentator “a sleepy son of a bitch”.

And just for good measure he defended Americans’ right to own guns, attacked Europe’s trade barriers and aired a fantasy wish to see convicted drug dealers sent to the gallows.

Trump’s appearance on Saturday (US time) was aimed at helping Republican Rick Saccone in a district Trump won overwhelmingly in 2016 as part of a narrow win in Pennsylvania. The latest polls show the race as a neck-and-neck contest – in part a reflection of voters’ weariness with Trump’s antics, pollsters say.

While he heartily endorsed Saccone as a “really good person,” Trump spent much of his time on stage in the packed-to-capacity hangar at Pittsburgh International Airport taking shots at Democrats and, as always, talking about himself.

In a seemingly largely unscripted hour-long address, Trump said he longed to run for re-election against Oprah Winfrey – a possibility the entertainer has ruled out.

“I’d love to beat Oprah,” Trump said, adding with a sly smile, “I know her weakness.”

NBC commentator Chuck Todd, host of the prestigious TV talk show Meet the Press on the NBC network, also copped a blast when Trump recalled being interviewed by the veteran journalist in 1999.

At that appearance he said President Bill Clinton should have “taken out” North Korea’s leaders instead of giving the Pyongyang regime “billions of dollars” as an inducement to abandon its nuclear program.

Calling the journalist, “Sleepy eyes Chuck Todd”, Trump then added, “He’s a sleeping son of a bitch.”

Under pressure over a brewing scandal involving porn star Stormy Daniels, Trump singled out his wife, Melania, for praise.

“You think her life is so easy folks? Not so easy,” he said.

Trump said the country should discuss having drug dealers face the death penalty because they are responsible for thousands of deaths.

“I don’t know if that’s popular. I don’t know if that’s unpopular,” he added.

A day after getting news that the US economy generated 313,000 fresh jobs in February, Trump said his 25 per cent tariffs on steel imports will boost Pennsylvania’s economy.

“Your steel is coming back – it’s all coming back,” Trump told the cheering crowd.

Critics say the tariffs could trigger retaliatory trade measures and damage the US economy. There are also doubts about how far Trump’s policies will go toward resuscitating the battered American steel industry.

He said it was crucial for Republicans to muster forces to turn back a strong Democratic drive to win one or both houses of the US Congress in November midterm elections.

“We need Republicans. We need the vote,” Trump said, saying Democrats would take away, among other things, “your Second Amendment rights” to bear firearms.

A Saccone defeat would be the first loss of a Republican seat in the House of Representatives since Trump took office, although Republicans would still control of the chamber.

-with AAP