Billionaire philanthropist and impeachment activist Tom Steyer entered the Democratic presidential race Tuesday, bringing the number of candidates back to 25, after Rep. Eric Swalwell’s withdrawal Monday.

Steyer spent more than $100 million to elect Democratic candidates in last year’s midterm elections and has pledged to spend $100 million on his own presidential campaign. He also has spent millions of dollars on an initiative encouraging Americans to back the impeachment of President Donald Trump.

Initially scheduling an announcement in January to enter the race, Steyer at the time declined to run, saying instead he wanted to focus his efforts on building support for impeachment. Steyer has reversed that decision, and on Tuesday placed an ad-buy in Iowa, New Hampshire, South Carolina and Nevada of more than $1 million to support his candidacy.

By far the wealthiest Democrat in the presidential race, Steyer has an estimated net worth of $1.6 billion, according to Forbes. He built his wealth running a hedge fund for 26 years before turning to politics and philanthropy.

The last Iowa poll that included Steyer before he initially ruled himself out of the presidential race at the start of the year found him as the first choice of 0% of likely caucus-goers and the second choice of 1%.

In order to qualify for the presidential debate stage later this month, Steyer will have to register at least 1% support in three Democratic National Committee approved polls, or receive 65,000 unique donations from at least 200 unique donors in at least 20 states.