Special counsel Robert Mueller and his team have reportedly taken an interest in President Donald Trump’s business ventures in Moscow before his 2016 presidential run.

Three people familiar with Mueller’s investigation have told CNN’s Kara Scannell, Pamela Brown, Gloria Borger, and Jim Sciutto that the special counsel has started questioning witnesses about Trump’s dealings in Russia — specifically the fate of a Trump Tower in Moscow — and when exactly Trump made the decision to run for president. Mueller may also be digging into whether there’s any compromising information on Trump that might connect the two, one source speculated to CNN.

The White House and the special counsel’s office declined to comment to CNN. Vox reached out to the White House for comment as well. But the president has previously indicated that his finances are a violation of the special counsel’s mandate. Trump, who has toyed with firing Mueller before, might once again target the special counsel if the investigation deepens into his finances.

Mueller is interested in when Trump wanted to run for president — and his 2013 Moscow trip

Mueller’s team is trying to pinpoint when Trump became serious about a presidential run, and if it might coincide with any sketchy business dealings. A source told CNN that “a witness told Mueller’s team his impression was that Trump was serious about running back in 2014,” and that Mueller’s team also wanted to know if Russians had visited Trump Tower in New York before 2015. This unnamed witness reportedly said no.

Trump’s 2013 trip to Moscow for the Miss Universe pageant has attracted much attention in the Russia scandal — and the CNN report says that Mueller also put it under scrutiny. Investigators are interested in who Trump met with during his time there.

That Russia visit has long been an odd bullet point in the Trump-Russia saga — one that has continued to pop up because the Russian financiers who helped bankroll the pageant helped arrange the infamous 2016 Trump Tower meeting with Don Jr. regarding promised dirt on Hillary Clinton.

The CNN report suggests that Mueller is also interested in the scrapped plans for a Trump Tower in Moscow — both the one in 2013 connected to the Miss Universe pageant and a renewed attempt led by Trump Organization lawyer Michael Cohen in 2015. (Cohen says he ended negotiations in January 2016.)

What’s more, Mueller’s alleged line of questioning, particularly when it comes to seeking “compromising” information on the president, echoes some of the allegations made in the unverified Steele dossier — the opposition research funded by the Clinton campaign that has been at the center of the controversy over the Nunes memo and FISA surveillance of former Trump campaign aide Carter Page.

Taken together, this turn in Mueller’s investigation may intensify Trump’s antipathy toward what he calls the “Russia hoax.” Trump has said that his finances are outside of Mueller’s purview, and could possibly put Mueller’s job in Trump’s crosshairs once again.