WASHINGTON (REUTERS) - Billionaire environmental activist Tom Steyer, who has spent millions on national ads calling for the impeachment of President Donald Trump, will spend US$30 million (S$40 million) this year trying to help Democrats win control of the US House of Representatives, he announced on Monday (Jan 8).

The former hedge fund manager, who told reporters he will not personally run for office in 2018, said he will also continue his national campaign calling for impeachment.

"My fight is in removing Donald Trump from office and removing Donald Trump from power," Steyer said.

The House impeaches, or brings formal charges against an official, in what would be the first step in removing Trump from office. The US Senate tries the case.

Steyer said his organisation is working to have constituents deliver to members of Congress copies of the controversial book Fire and Fury: Inside the Trump White House by Michael Wolff, which challenges Trump's fitness for office.

Steyer will not, however, require House candidates whom he supports to pass a "litmus test" supporting impeaching Trump, he said.

The US$30 million will be used to mobilise young voters in 10 key states: Florida, Virginia, Wisconsin, Michigan, Nevada, California, Pennsylvania, Iowa, New Hampshire and Arizona, Steyer said.

Americans will head to the polls in November when 34 seats in the Senate and all 435 House seats will be up for grabs. Democrats are hoping to ride wins last year in Alabama and Virginia to victory in those elections, potentially taking control of Congress from Republicans.

"The task which I feel called to do is organising and mobilising America's voters - they have got to be the most powerful forces in American politics," Steyer said at a Washington press conference.

The Republican National Committee dismissed Steyer's spending saying he could "light as much of his money on fire as he wants," arguing that Democrats have criticised his impeachment message as a distraction.

"If Democrats' message for 2018 is a baseless impeachment threat that the majority of voters disagree with, they're going to lose," said RNC spokesman Michael Ahrens in a statement.

Steyer said he knows that some Democrats think talking about impeachment is a distraction but that he feels it remains important to focus on ousting Trump.

"We know this makes some of our friends and allies in this city uncomfortable," Steyer said. "We believe this is a false choice - the fact is the two are fundamentally intertwined."