But inside the crowded hall, another retired teacher, Barbara Tymrakiewicz, brought a sign bearing the opposite message.

“We’ve got your back, Representative Slotkin,” it said.

For Ms. Slotkin, Monday’s meeting — and Wednesday’s impeachment vote — will be the culmination of an extraordinarily tumultuous first year on Capitol Hill. She arrived in January, a long-shot candidate having been swept into office on a Democratic wave, eager to make good on her central promise: to lower the cost of prescription drugs. She had avoided talk of impeachment, promised to be bipartisan and voted against Nancy Pelosi for speaker of the House.

But the impeachment question hovered in the background. On her first day in office, Ms. Slotkin’s fellow Michigan freshman, Representative Rashida Tlaib, was caught on video using a vulgarity to describe how she wanted to impeach Mr. Trump. Ms. Slotkin was asked what she thought.

“I didn’t love it,” she said.

Soon the Republican “tracker” who follows Ms. Slotkin with a video camera during her public events began trying to goad her into addressing impeachment. She ignored him.

But the pressure really began to build in the spring, she said, when Mr. Mueller released his report on Russian interference in the 2016 election, and outlined at least 10 instances in which Mr. Trump tried to obstruct the investigation. Progressive activists and even some Democratic colleagues pushed her to call for an impeachment inquiry.

Ms. Slotkin was unpersuaded. “For me, the decision to call for an impeachment is such a big deal,” she said. “And you have to bring the country along with you. That was an important piece for me.”

Instead of seizing on the obstruction issue, she focused on the election interference, convening a task force to draft legislation aimed at securing the 2020 balloting. So when news broke that the president had tried to enlist a foreign power, Ukraine, to investigate his political rivals in a way that could affect a future election, Ms. Slotkin said, she could no longer avoid the topic.