President Trump apparently sees Facebook CEO Mark Zuckerberg as a threat to his reelection campaign in 2020.

Zuckerberg is a part of a list of potential 2020 Democratic challengers whom Trump is watching, Politico reported Monday. The list includes dozens of individuals who could throw their hat in the ring for the presidential race, including Sen. Elizabeth Warren Elizabeth WarrenGOP set to release controversial Biden report Biden's fiscal program: What is the likely market impact? Warren, Schumer introduce plan for next president to cancel ,000 in student debt MORE (D-Mass.).

On the Republican side, Trump allies are reportedly keeping an eye on a possible primary challenge from Ohio Gov. John Kasich.

Speculation about the Facebook CEO’s presidential aspirations have mushroomed since he announced that he would visit all 50 states in 2017, meeting community members and leaders in each one. The media, political consultants and other observers immediately compared Zuckerberg’s trips to speaking tours that presidential hopefuls often embark on before announcing their candidacies.

Zuckerberg had previously sparked rumors of a future bid for political office when, in May 2016, Facebook created a class of company shares that would let Zuckerberg retain control of the company even if he were “serving in a government position or office.”

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Since the speaking tour, he has continued to fuel speculation of a presidential run by releasing posts advocating for political positions like

universal basic income

. In May, he delivered a politically tinged

commencement speech

at Harvard advocating for “a new social contract,” arguing about policies on climate change, prison reform, job automation and healthcare.

When asked for comment, a Facebook spokesperson noted that Zuckerberg has said “multiple times he's not running.” He most recently denied his interest in a 2020 bid in May, writing that his purpose for the 50-state tour was not to bolster a bid for public office, but “to get a broader perspective to make sure we're best serving our community of almost 2 billion people at Facebook and doing the best work to promote equal opportunity at the Chan Zuckerberg Initiative.”

Facebook, like many technology companies, has clashed with Trump’s administration since the real estate mogul took office. The two have battled over the president's proposed policy of keeping foreign nationals from six predominantly Muslim countries out of the U.S. temporarily and on Trump’s decision to back out of the Paris climate agreement.

The White House has also pushed back against the company. Before his departure from the White House on Friday, an Intercept report in July revealed that former chief strategist Stephen Bannon had been pushing to regulate internet companies like Facebook and Google as public utilities.