Minnesota police officers responding to a reported break-in last year found a state lawmaker in her stepmother’s basement, dressed in black and carrying a flashlight covered with a sock.

The pre-dawn arrest of that legislator, State Senator Nicole Mitchell, a Democrat, brought felony charges and calls from Republicans for her to resign or face expulsion. But Ms. Mitchell maintained her innocence, and her fellow Democrats, who hold a one-seat Senate majority, continued to rely on her vote as the case against her moved forward.

On Friday, a jury in northern Minnesota convicted Ms. Mitchell of burglary and possession of burglary or theft tools, felonies that can carry prison sentences. The verdict, which came after a weeklong trial, raised new questions about whether Ms. Mitchell would continue to serve, and how many Democrats might now join Republicans in seeking her resignation or removal.

The case was watched closely because both chambers of the Minnesota Legislature are narrowly split between Republicans and Democrats, and a series of circumstances, including Ms. Mitchell’s trial, have tested those margins.

Already this year, special elections have been held to replace a Democratic senator who died and a Republican senator who resigned after being accused of arranging to meet with an underage prostitute. Another special election filled a House seat after a judge determined that the Democrat who won the regular election did not meet residency requirements. Then last month, State Representative Melissa Hortman, a Democrat, was assassinated and State Senator John A. Hoffman, a Democrat, was shot and wounded in what the authorities described as targeted political violence.

If Ms. Mitchell leaves office, the Senate would be evenly divided until Gov. Tim Walz, a Democrat, calls a special election for voters to choose a replacement, which could happen before lawmakers return to the Capitol in 2026.