Democrats face a tough fight in the Nov. 5 election preserving their narrow 51-49 majority in the U.S. Senate, as they are defending several incumbents in Republican-leaning states.

Utah Republicans on Tuesday will nominate a contender to seek retiring U.S. Senator Mitt Romney’s seat. Below are some Senate races to watch:

Utah: Crowded Republican primary

Utah is an open seat, with Romney, a prominent Trump critic and onetime party presidential nominee, having said he will not seek reelection. Unlikely to swing to Democratic hands, the state is expected to feature a crowded Republican primary field.

Republicans seeking the seat include the former speaker of the state’s House of Representatives, Brad Wilson and U.S. Representative John Curtis.

Utah’s primaries will be held on June 25.

Arizona: Sinema drops out

Democrat-turned-independent Kyrsten Sinema said on March 5 she would not seek reelection in Arizona, reducing the risk of a three-way race and setting the stage for Democratic U.S. Representative Ruben Gallego, a progressive, to face off against a Republican candidate.

The Republicans seeking the nomination include Kari Lake, who had been endorsed by Trump during her unsuccessful 2022 run for governor, and Mark Lamb, a county sheriff.

Though Lake is considered the leading candidate and has amassed endorsements from some Senate Republicans, she has also been embroiled in disputes with other Republicans, including the former head of the state Republican Party.

Arizona’s primaries will be held on July 30.

Michigan: Crowded race for open seat

With Democratic Senator Debbie Stabenow retiring, Michigan’s Senate race is poised to be competitive in a Midwestern state that is also expected to play a key role in the presidential election.

Representative Elissa Slotkin, a former CIA analyst who currently represents a swath of communities west of Detroit, is the clear favorite for the Democratic nomination. She will face off against Hill Harper, an actor who appeared on the popular television show “The Good Doctor.”

The candidates vying for the Republican nomination include former lawmakers Mike Rogers, who headed the House Intelligence Committee, and Justin Amash, a founding member of the House Freedom Caucus who broke with his party to call for Trump’s impeachment.

Michigan’s primaries will take place on Aug. 6.

Wisconsin: Republicans take on Baldwin

Democrat Tammy Baldwin is seeking a third term in a state that is expected to be competitive. Eight Republicans and independents have filed to run against her.

The leading candidate for the Republican nomination is Eric Hovde, a wealthy banker who has drawn scrutiny for remarks about the voting capabilities of nursing home residents.

Wisconsin will hold its primaries on Aug. 13.

New Jersey: Looking to replace Menendez

Democratic U.S. Representative Andy Kim handily won the nomination in his bid to succeed Senator Bob Menendez.

Menendez, who is on trial by federal prosecutors for bribery and obstruction of justice charges, was not on the Democratic ballot and is running for reelection as an independent.

Curtis Bashaw, a hotelier, won the Republican nomination.

Democrats are strongly favored to hold the seat in November.

Montana: Vulnerable Democratic incumbent

Democrat Jon Tester is defending his seat, which he has held since 2007, in a Western state that backed Trump during the 2020 election.

Tim Sheehy, a former Navy SEAL who founded an aerial firefighting company, won the June 4 Republican primary to take him on.

Nevada: Rosen fights to stay on

Jacky Rosen, a Democrat, is running for a second six-year term in the Senate. The race is expected to be competitive, and 16 people have filed to challenge her, nine of them Republicans.

Sam Brown, a military veteran who received a Purple Heart after being wounded by a roadside bomb in Afghanistan, won the crowded Republican primary to take her on.

—Makini Brice, Reuters