Milwaukee sheriff David Clarke has resigned

Milwaukee County Sheriff David Clarke speaks during the opening day of the Republican National Convention in Cleveland, on July 18, 2017.

AP

Last Updated Aug 31, 2017 6:03 PM EDT

Controversial Milwaukee County Sheriff David Clarke has resigned, the Milwaukee County Clerk told CBS affiliate WDJT.

The resignation will go into effect at 11:59 p.m. Thursday, Milwaukee County Clerk George L. Christenson told CBS News.

Christenson said Thursday that he received a resignation letter from Clarke. Christenson says the letter didn't give the reason for Clarke's resignation. 

In a statement, Clarke said he was leaving "to pursue other opportunities." He said he will have "news about my next steps in the very near future."

Clarke rose to national prominence in recent years with provocative social media posts, appearances on conservative media programs and his staunch support of President Trump. Clarke announced in May that he'd taken a job at the Department of Homeland Security, but the agency never confirmed it. He later said he withdrew his name

Sources confirmed to CBS News that Clarke is not joining the Department of Homeland Security.  

Some Wisconsin conservatives had encouraged Clarke to challenge U.S. Sen. Tammy Baldwin, a Democrat, but he repeatedly rejected their overtures.

Clarke recently published a memoir, "Cop Under Fire." On Sunday, Mr. Trump tweeted support for Clark and his book, calling it "a great book by a great guy."

Clarke has drawn a considerable amount of controversy as Milwaukee County sheriff.

He was hit by allegations in May that he plagiarized content in his master's thesis on homeland security, which he denied.

Seven workers at the county jail he oversees are at the center of a criminal investigation into the dehydration death last year of an inmate who prosecutors say was deprived of water as punishment. Clarke isn't among the seven staffers — prosecutors said he wasn't directly involved in the events that led to the death of 38-year-old Terrill Thomas — but the death happened under Clarke's leadership, which his critics say is enough cause for his firing.

Clarke was one of the few African-Americans to speak at the Republican Party national convention last year. He has been vocal about gun rights and critical of what he called the "hateful ideology" of the Black Lives Matter movement, saying at times, "Stop trying to fix the police, fix the ghetto." During his speech, Clarke told the crowd that the movement is a form of "anarchy," CBS New York reported.

Clark has been sheriff of Milwaukee County since 2002 and spent more than two decades before that with the city's police department. In a statement, Gov. Scott Walker said they will move forward with filling the position as soon as they are formally notified. The new sheriff will hold the position until the 2018 election, WDJT reports.