PITTSBURGH, Sept 26, 2024 (BSS/AFP) - Kamala Harris blasted Donald Trump as the "biggest loser" on the economy and a friend of billionaires Wednesday as the election rivals laid out competing plans on the top issue for many US voters.

In a speech on the economy and then again in her first major solo interview, the Democrat warned that Trump's plans to bring back huge tariffs on foreign imports would hurt middle class Americans in their wallets.

Republican Trump for his part doubled down on his protectionist vision -- but spent as much time on threatening to blow Iran to "smithereens" after US intelligence warned of threats from Tehran against his life.

The vice president and the former president are neck-and-neck in the polls and are both reaching out to undecided voters on key issues like the economy with less than six weeks until election day.

Harris vowed to "chart a new way forward" in a speech in Pittsburgh, an industrial city in the critical swing state of Pennsylvania, with her rhetoric focusing on lowering prices for Americans.

"For Donald Trump, our economy works best if it works for those who own the big skyscrapers. Not those who actually build them. Not those who wire them. Not those who mop the floors," she said.

She said nearly 200,000 factory jobs moved abroad during Trump's time in the White House, "making Trump one of the biggest losers ever on manufacturing."

In her interview with the left-leaning MSNBC, Harris then criticized the tariff plans that Trump has laid out over the past two days, which would be a return to the policies of the Republican's first term in office.

"You don't just throw around the idea of tariffs across the board," said Harris. "He's just not very serious."

The interview was Harris's first on her own since replacing US President Joe Biden as the Democratic nominee in July. She gave a joint interview with running mate Tim Walz in August.

- 'Smithereens' -

Trump's campaign said her speech was "full of lies" and that she had already had three and a half years as part of the Biden administration to tackle problems like low prices.

The Republican is making similar pledges to boost American manufacturing, based largely on his plans to impose sweeping tariffs on foreign imports.

"You're going to have protection from them coming in, because we're going to put on from 50 to 200 percent tariffs," Trump told supporters in Mint Hill, North Carolina -- another crucial battleground state.

But the ex-commander-in-chief spent a good part of his speech talking about the threats to his life -- from the two assassination attempts he has escaped in the space of two months to threats by Iran.

"If I were the president, I would inform the threatening country, in this case Iran, that if you do anything to harm this person, we are going to blow your largest cities and the country itself to smithereens," Trump said.

Trump meanwhile plans to return on October 5 to the Pennsylvania town of Butler where a gunman made an attempt on his life at a rally in July, his campaign said Wednesday.

A gunman accused of planning to kill Trump at his Florida golf course just over a week ago, Ryan Routh, was indicted Tuesday for the attempted assassination of a major presidential candidate.

The twin assassination attempts came amid one of the most dramatic US election campaigns in modern political history, in a dizzying chain of events since a disastrous debate in June led to Biden quitting the White House race over concerns about his age.

Biden told ABC talk show "The View" on Wednesday that he was now "at peace with my decision" -- even if he insisted he could still have beaten Trump.

The outgoing president criticized Trump, saying there was "not a social redeeming value" to the Republican, and said his advice to Harris to win was to "be herself."