Southern Baptists are poised to vote at their annual meeting Tuesday and Wednesday on whether to crack down on women in pastoral leadership and whether to condemn the use of in vitro fertilization, setting up a referendum on the role of women in the nation’s largest Protestant denomination and in American society.

With almost 13 million church members across the United States, the Southern Baptist Convention has long been a bellwether for American evangelicalism. Its reliably conservative membership makes it a powerful political force, and its debates have attracted widespread interest from outside pundits and politicians this year. The denomination has experienced the same turmoil over politics and priorities that has divided the conservative movement more broadly in the wake of the 2016 election of Donald J. Trump as president.

“I hope every single person in this room is voting not only in November but is voting tomorrow because of what is at stake in the Southern Baptist Convention,” Ryan Helfenbein, the executive director of a think tank at Liberty University, told attendees at a lunch on Monday in Indianapolis near where the annual meeting will take place.

Mr. Trump recorded a brief message for the “very respected people” gathered at the lunch, which was hosted by the Danbury Institute, a new conservative Christian advocacy group with Southern Baptist ties.

“You just can’t vote Democrat,” Mr. Trump said in the video message, which some attendees had waited two hours to hear. “They’re against religion, they’re against your religion in particular.” He assured them that under a second Trump presidency, “you’re going to make a comeback like just about no other group.”

Delegates, known as “messengers,” include male pastors from the more than 45,000 Southern Baptist churches across the country as well as many church and staff members, including women.