The Trump administration’s stated rationale for firing FBI Director James Comey Tuesday was that he overstepped the bounds of his office during the Hillary Clinton email investigation last year.

The Wall Street Journal and Politico are reporting, however, that Trump was increasingly furious with Comey because of the bureau’s investigation into any possible collusion between Russia and the Trump campaign during last year’s presidential election. Here’s Politico:

“[Trump] had grown enraged by the Russia investigation, two advisers said, frustrated by his inability to control the mushrooming narrative around Russia. He repeatedly asked aides why the Russia investigation wouldn’t disappear and demanded they speak out for him. He would sometimes scream at television clips about the probe, one adviser said.”

Both news outlets report that Trump grew especially angry while watching Comey’s televised appearances before congressional panels, and his administration wanted the director to publicly swat down suggestions of ties to Russia. Comey did not.

In the short letter Trump sent to Comey terminating him, the president made a point of thanking the director for “informing me, on three separate occasions, that I am not under investigation.” That has not been confirmed by the FBI — and would be highly unorthodox for Comey to do — but it suggests that the Russia investigation was top-of-mind for Trump.