Billionaire donor and liberal activist Tom Steyer, who has led an effort to impeach President Donald Trump, announced on Wednesday he will not seek the Democratic presidential nomination and instead will continue his effort to oust the president.Steyer, 61, made his announcement in Iowa, the traditional starting point for the presidential nominating contests that will kick off early next year, after months of openly exploring his own presidential campaign, his staff confirmed."The impeachment question has reached an inflection point," Steyer wrote on Twitter. "That's why I just announced that I will be dedicating 100% of my time and effort in 2019 towards Mr. Trump's impeachment and removal from office."Steyer's decision not to enter the race also leaves the deep-pocketed donor available to support one of as many as two dozen Democrats who are weighing 2020 presidential bids if he chooses.Steyer has been a force in Democratic fundraising over the past decade. NextGen America, a political nonprofit he formed in 2013, has poured millions into elections, focusing on climate change, immigration and access to affordable healthcare, among other issues.Steyer said he spent $120 million on the 2018 congressional elections, investing heavily in youth turnout, which he called an untapped source of Democratic support. He also spent more than $90 million during the 2016 elections, when he backed Democratic presidential nominee Hillary Clinton.Some of his money has gone to his Need to Impeach campaign against Trump. Steyer has accused the Republican president of colluding with Russia to win the White House in 2016 and obstructing investigations into their efforts, allegations that Trump has denied.In a video on Twitter on Tuesday, Steyer accused Trump of "holding America hostage" over his insistence on funding for a wall along the U.S.-Mexico border. An impasse over the funding between Trump and Democratic congressional leaders has led to a 19-day-old partial government shutdown."It’s time for this man to go," Steyer said.In a tweet in October, Trump dismissed Steyer as a "crazed & stumbling lunatic who should be running out of money pretty soon."Steyer amassed a fortune estimated by Forbes at $1.6 billion by founding the investment firm Farallon Capital in the mid-1980s and serving as a partner at the San Francisco private equity firm Hellman & Friedman.Early opinion polls showed the environmentalist and philanthropist, who is based in San Francisco, trailing other Democrats in name recognition and support.