ST. PAUL, Minn. (AP) — A high-ranking Minnesota state lawmaker thrust into the lieutenant governor's office following U.S. Sen. Al Franken's resignation moved abruptly Friday to resign her state Senate seat and take the oath of office as lieutenant governor, a swift reversal for the longtime Republican senator who had resisted the job and its duties.

Senate President Michelle Fischbach's ascent was automatic after Democratic Gov. Mark Dayton appointed then-Lt. Gov. Tina Smith to U.S. Senate following Franken's resignation amid a sexual misconduct scandal. Guarding a one-seat majority in the Senate, Fischbach and fellow Republicans insisted she could remain in the Senate even after being elevated to lieutenant governor.

Her decision to resign from the chamber averts a second lawsuit from a constituent challenging Fischbach's dual roles. But it also triggers the sole state Senate election of the fall, a contest that will determine control of Senate. The rest of the state's 66 Senate districts aren't on the ballot until 2020.

Gov. Mark Dayton's office said Fischbach will formally resign her central Minnesota Senate on Friday. Dayton plans to call a special election for the seat coinciding with the Nov. 6 general election.

Fischbach did not immediately respond to messages seeking comment from The Associated Press.

Fischbach had avoided taking the oath and fought a pair of legal challenges since she ascended to become Dayton's lieutenant governor on Jan. 3, as she clung to her Senate seat.

While she and fellow Senate Republicans argued there was plenty of historical precedent for a presiding officer of the Senate also serving as lieutenant governor, Democrats called it a blatant constitutional violation of the ban on holding two elected offices.

An initial lawsuit filed by Democratic constituent Destiny Dusosky was dismissed earlier this year, in large part because it was filed before the Legislature resumed its session — and thus before Fischbach had carried out both roles. Dusosky followed up with a second challenge in April. That case was awaiting a hearing scheduled for June 5.

The legal challenge had heavy implications, as Fischbach gave Republicans a one-seat edge in the Senate. Whether forced by the courts or voluntary, her exit triggers a high-stakes election that will determine control of the Senate. Her central Minnesota district is heavily Republican, and GOP leaders scoffed at the notion that Democrats could win it.

Minnesota Public Radio News reports Fischbach told colleagues in an email she would not run for the seat she has held since 1996. She had previously indicated she would run in a special election if she were forced from her seat.

Her resignation will temporarily leave the Senate deadlocked at 33-33 until January. Lawmakers wrapped up their work for the year at midnight Sunday.