Steven Mnuchin will be overshadowed during his first congressional testimony as Treasury secretary on Thursday by a deepening political crisis at the White House that threatens his aspirations for tax and regulatory overhauls.

President Donald Trump’s firing of FBI director James Comey and the aftermath is beginning to color all business in Congress, especially after the emergence on Tuesday of a memo Comey wrote in which he said Trump tried to end an investigation of links between his associates and the Russian government. Democrats have raised the specter that Trump attempted to obstruct justice, an impeachable offense.

Mnuchin’s testimony before the Senate Banking Committee was previously scheduled, and he is unconnected to the Comey controversy. But the questions he faces — especially from Democrats — aren’t likely to remain confined to Mnuchin’s plans to ease Wall Street regulations and pass what he’s called an historic tax overhaul.

Democrats may ask