SALT LAKE CITY — Representative Jason Chaffetz revealed Thursday he will resign from Congress next month, saying a ‘‘midlife crisis’’ compelled him to step away from his chairmanship of the House Oversight Committee as it is poised to launch an investigation into President Trump’s firing of the FBI director.

The announcement by Chaffetz, 50, was the latest upending of the Republican-controlled congressional investigations into Trump.

The news came a day after Chaffetz tweeted that he had invited ex-FBI director James Comey to testify next week at a hearing of the oversight committee.

Comey was fired last week amid an FBI investigation into whether Trump’s presidential campaign associates colluded with Russia to influence the presidential election outcome to benefit him.

Chaffetz, a Utah Republican who had just started his fifth term in Congress, used his post as chairman of the oversight committee to doggedly investigate Hillary Clinton before the 2016 presidential election and raise his political profile.

But Trump complicated Chaffetz’s life. He rescinded his endorsement of Trump last year after recordings surfaced of the reality show star bragging about groping women, only to hastily re-endorse Trump shortly before the FBI announced it was reviving its investigation into Clinton’s e-mails.

After Trump won the election, Chaffetz became a lightning rod for criticism that Republicans weren’t aggressively policing Trump.

Liberals said that he did not go after the incoming administration with nearly the vigor used against the prior Democratic administration. Constituents booed him at a raucous February town hall, and a novice Democratic candidate raked in hundreds of thousands of dollars in online donations when she announced her longshot challenge to him weeks later.

Last month, Chaffetz stunned the political world by saying he would leave Congress before his current term ends in 2018.

But he did not provide a date for his departure until Thursday.