There's a good legal case that Republican state Senate President Michelle Fischbach can't hold her legislative job and be Minnesota's new lieutenant governor, according to an advisory opinion made public Thursday by DFL Attorney General Lori Swanson's office.

"The simultaneous discharge of executive and legislative branch functions implicates the incompatibility doctrine, as well as principles of separation of powers," Solicitor General Alan Gilbert wrote, while saying final resolution would come from judicial branch.

The analysis has no binding authority. It was done upon request of DFL Gov. Mark Dayton, whose intention to appoint Lt. Gov. Tina Smith to the U.S. Senate will trigger a succession that could throw the state Senate into a temporary tie. Smith will have to resign upon taking her oath in Washington on Jan. 3, if not before.

Republicans and Democrats have competing views of whether Fischbach, R-Paynesville, could remain in the Senate — and thereby keep the GOP's slim majority — or whether she'll have to leave upon moving up after an automatic ascension to lieutenant governor.

The differing views likely mean the dispute is headed to court, in large part because Senate Democrats feel they have a chance to win majority control if a Democrat wins the seat they believe the court would require Fischbach to leave.

Full coverage: Politics

Republicans point to an 1898 Minnesota Supreme Court opinion and past precedent to argue it's possible to serve in two branches of government at once. Democrats cite constitutional amendments from 1968 and 1972 for their view that she can't do double duty.

DFL leaders have so far turned back overtures from Republicans to hold a special session to install a DFL lawmaker in the president's post for purposes of succession.

Can she do that? New MN lieutenant gov. wants to keep Senate seat, too

Senate Minority Leader Tom Bakk, DFL-Cook, said in an interview earlier Thursday that he was bracing for the potential of a 33-33 tie when the 2018 session begins on Feb. 20.

That would depend on his party retaining a suburban seat that had been held by Dan Schoen, who resigned last week amid sexual harassment allegations. The special election to fill that seat is set for Feb. 12.

"I don't know how firm (Fischbach) is about wanting to hold both positions, but the way I look at the constitution I'd be very surprised if she could do that," Bakk said, adding that a lawsuit to remove her would be possible.

But Senate Majority Leader Paul Gazelka, R-Nisswa, said the opinion from Swanson's office doesn't change anything.

"I have every confidence Sen. Fischbach will continue to be an effective public servant for her constituents in her roles as a state senator for District 13 and acting lieutenant governor of Minnesota."

Dayton said Thursday a legal challenge wouldn't come from him, saying it's a matter for the Senate to resolve.

"I'm not going to call a special election for something where I have not received a resignation," he said. "That has been my consistent practice throughout."

If the Senate does move into a tie, it would require either a power-sharing arrangement between the parties or gum up the works for what is supposed to be a short, election-year session.

Bakk said four people have expressed interest in running in the Paynesville-St. Joseph-area district for the Democrats if there is a special election.

He said former state Rep. Larry Hosch is the only one he has spoken to, but it's unclear if Hosch would seek to return to the Legislature after leaving in 2012 to spend more time with his young family.

For Democrats, the Fischbach promotion comes with some risk. It would put a Republican a step from moving into the governor's office and gaining complete control of state government if something makes Dayton unable to complete his term. The 70-year-old governor has had health complications but said he is geared up to serve out his last year.

Attorney General Lori Swanson's advisory opinion