Sen. Dianne Feinstein said Thursday that a “bad cold” possibly attributed to her decision not to tell Senate Judiciary Chairman Charles E. Grassley about the release of Glenn Simpson’s testimony earlier this week.

“The one regret I have is that I should have spoke with Senator Grassley before. And I don’t make an excuse, but I’ve had a bad cold and maybe that slowed down my mental facilities a little bit,” Ms. Feinstein, California Democrat, told NBC News.

Mr. Simpson is the co-founder of Fusion GPS, the research firm hired to gather information on then-candidate Donald Trump. The result was an unverified dossier written by former British intelligence officer Christopher Steele. Republicans have said the dossier was politically motivated and used to obtain FISA warrants to spy on Mr. Trump’s campaign.

Ms. Feinstein said in a statement earlier this week that she released the transcript to fight back against this narrative.

“The innuendo and misinformation circulating about the transcript are part of a deeply troubling effort to undermine the investigation into potential collusion and obstruction of justice,” Ms. Feinstein said in a statement.