Last summer, Donald Trump cautioned that Robert Mueller would be crossing a red line if he began digging into his family’s finances. “I think that’s a violation. Look, this is about Russia,” Trump said at the time. Mueller, however, seems to believe that questions surrounding Trump’s business deals and Russian ties are intertwined. The day after Trump issued his ultimatum, reports emerged that the special counsel was, in fact, probing his overseas business transactions. But the president backed down, allowing Mueller to continue his investigation. And Mueller, unbowed, has kept digging.

Seven months later, CNN reports that Mueller has expanded his inquiry to include Russia’s potential leverage over the president and why he decided to run for president. According to sources who spoke to CNN, F.B.I. investigators have questioned witnesses about whether Trump showed an interest in running for president as far back as 2014, and how that desire coincided with his business ventures in Russia. The new line of inquiry confirms that Mueller is not just investigating potential obstruction of justice, but also allegations of collusion between the Trump campaign and Russia.

It is unclear whether Mueller is pursuing any hardened leads. “You ask everything even if you don’t think it’s credible,” one of the sources told CNN. “The allegations are out there, and it was checking the box.” Still, there are reasons to believe that the origins of Trump’s campaign might intersect with his financial interests in Russia. In late 2015, for example, Russian-born developer Felix Sater e-mailed Trump lawyer Michael Cohen to boast that they would soon be celebrating both Trump’s election and a major new real-estate deal in Moscow. “I will get Putin on this program and we will get Donald elected,” he wrote Cohen, suggesting the two goals were connected. “I know how to play it and we will get this done. Buddy our boy can become president of the USA and we can engineer it. I will get all of Putin’s team to buy in on this.”

Trump’s business interests in Russia predate 2015, of course. In 2008, the president’s eldest son, Donald Trump Jr., bragged that “Russians make up a pretty disproportionate cross-section of a lot of our assets. We see a lot of money pouring in from Russia.” In 2013, Trump partnered with Russian real-estate developer Aras Agalarov and his son, Emin Agalarov, to bring the Miss Universe pageant to Moscow. Three years later, Emin Agalrov would help arrange the infamous Trump Tower meeting between Don Jr. and a Russian lawyer peddling dirt on Clinton.

Mueller is particularly interested in the pageant, according to CNN. One source said the special counsel was focused on uncovering the financing for the 2013 event, which the Trump Organization has never disclosed. Investigators reportedly pursued lines of questioning that led another source to believe they were looking into whether Trump could have been compromised during the pageant, and if the Russians possibly had “kompromat” on Trump, as detailed in the Steele dossier. Sater’s failed attempt to build a Trump Tower in Moscow has also raised red flags. Shortly after the 2013 pageant, Trump tweeted at Aras Agalarov, “TRUMP TOWER-MOSCOW is next.” The deal fell through after the United States imposed sanctions on Russia for invading Ukraine, but Cohen restarted negotiations in 2015, and Trump signed a letter of intent to proceed. (Cohen has said he ended the negotiations in early 2016.)

The revelation that Mueller is probing Trump’s business dealings in Russia comes on the heels of Rick Gates’s guilty plea on two relatively minor charges, in exchange for his cooperation. Gates is the third former Trump campaign aide to flip, joining the ranks of former national security adviser Mike Flynn and former foreign policy aide George Papadopoulos. All three could offer illuminating accounts of the Trump campaign’s inner workings, and Flynn and Gates, who stayed on after the campaign, were witness to key moments in the Trump White House.