City Council Speaker Corey Johnson, who had been gearing up to be the most high profile candidate to replace Mayor Bill de Blasio in 2021, announced on Thursday that he will not run for mayor.

Johnson spent the better part of his first two years as speaker in the public eye: dancing, issuing sweeping policy recommendations, and taking positions—on Fair Fares, on transportation, on homelessness, on policing—that were often at odds (and to the left) of the de Blasio administration's position. Johnson seemed to actually enjoy his job, unlike Mayor de Blasio, who embarked on a dead-end run for president. One headline from late 2018 said it plainly: "Is Corey Johnson Already Mayor?"

But since the global pandemic hit New York, and especially after a bruising City Council budget battle in July, during which Johnson oversaw a $1 billion reallocation of funds from the NYPD, the speaker has kept a relatively low profile.

"It was no secret that I had been considering a run for mayor, and that I have put my campaign on pause for the past six months," Johnson said in a statement. "This challenging time has led me to rethink how I can best be of service to this city, and I have come to the conclusion that this is not the right path for me."

Johnson, who has been open about his HIV status and past battles with addiction, gave another reason for his period of reflection.

"In the same spirit of openness, I would also add that I have been dealing with some personal challenges over the past few months, namely—depression," Johnson's statement reads. "Too often mental health issues are shrouded in secrecy and stigmas, which cause people struggling with those issues to feel alone. I encourage anyone who is experiencing a mental health condition to seek help. I did and I am better for it."

Johnson stressed that his career in public service isn't over but did not specify what that meant beyond finishing his term as speaker, which also ends in 2021.

Even without Johnson, the mayor's race is still expected to be relatively crowded. Comptroller Scott Stringer and former NYC Veteran’s Affairs Commissioner Loree Sutton have announced their candidacies. Other likely candidates include former Bloomberg and Obama administration official Shaun Donovan, former board chair of NYC Civilian Complaint Review Board Maya Wiley, former MSNBC Legal Affairs analyst and counsel to Mayor de Blasio, and de Blasio's former Sanitation Commissioner, Kathryn Garcia.