A little over a month later, Trump fired Preet Bharara, who had been the U.S. attorney for the Southern District of New York since 2009. Bharara was reportedly investigating Rep. Tom Price, then Trump's nominee for Health and Human Services secretary. It was a surprising move because in the weeks after the election, Trump met with Bharara and asked him to stay in his post. Bharara was fired March 11 after refusing to resign.
Then, on May 9, FBI Director James B. Comey was fired. He was in charge of the FBI's investigation into Russian interference in the 2016 election, and on March 20, he testified that the investigation included looking at contacts between the Trump campaign and Russian officials.
It's hard to say that the three officials were fired specifically because they were investigating Trump. In Yates's case, it seemed obvious she'd be fired as soon as she defied Trump's travel ban order; Bharara was set to be one of just a few U.S. attorneys who kept their posts from the Obama administration; and politicians on both sides of the aisle had called for Comey's resignation at various times since the election.
But in all three firings, there's a common thread: They were investigating Trump, his administration or campaign. And when firing the people who investigate the president becomes a pattern, it starts to look like Trump wants to avoid being investigated at all.