FILE PHOTO: Milwaukee County Sheriff David Clarke gestures after speaking at the Republican National Convention in Cleveland, Ohio, U.S. on July 18, 2016. REUTERS/Aaron Josefczyk/File Photo

(Reuters) - Wisconsin Sheriff David Clarke, an African-American who has criticized the Black Lives Matter movement and was previously under consideration for a position with the Trump administration, has quit his job, an adviser said on Thursday.

Clarke, 61, who spoke at the Republican National Convention last summer and campaigned for then-presidential candidate Donald Trump, submitted his resignation Thursday and will step down at the end of the day, political consultant Craig Peterson said in a telephone interview.

The 38-year law enforcement veteran was appointed Milwaukee County sheriff in 2002 and re-elected several times. Although he ran as a Democrat, he moved steadily to the right, and currently supports Trump “a thousand percent,” Peterson said.

“After almost 40 years serving the great people of Milwaukee County, I have chosen to retire to pursue other opportunities,” Clarke said in a statement published by the Milwaukee Journal Sentinel.

Although once under consideration for a position in the Trump administration, Peterson said that was unlikely now. He said Clarke was not doing media interviews on Thursday, but would announce his future plans next week.

Politico, citing two sources familiar with the matter, reported Clarke was still expected to take a job with the Trump administration. One of the sources told Politico he was expected to join the White House.

White House spokeswoman Natalie Strom said they had no announcement at this time regarding Clarke.

Clarke has become one of the most polarizing critics of the Black Lives Matter movement, which grew out of protests against police killings of unarmed black men.

Clarke said in May that he was taking a job as assistant secretary in the U.S. Department of Homeland Security, but the following month media reported that he had withdrawn his acceptance of the job.