Republicans are eyeing Arizona Democratic Rep. Kyrsten Sinema’s seat as a potential pickup opportunity in a cycle where they are largely on defense, now that she is opening up the seat to run for Senate.

Sinema’s Phoenix-area district decisively supported Democratic presidential nominee Hillary Clinton in 2016, but Republicans still view the race as competitive.

“Yet another House Democrat has vacated a competitive seat and the NRCC is ready to take advantage,” National Republican Congrsessional Committee spokesman Matt Gorman said. “The NRCC not only believes this seat is in play, but is a prime pickup opportunity in 2018.”

Clinton won the seat by 17 points in 2016, and former President Barack Obama won the district by four points in 2008 and 2012.

But the largest swath of voters, 35 percent, are not registered with either party. Democrats comprise 33 percent of registered voters while 31 percent are registered Republicans. Sinema, who was known as a liberal state legislator, tacked to the center while in Congress, securing her re-election in 2014 and 2016. Inside Elections with Nathan L. Gonzales rates the race Solid Democrat.

But without Sinema running again, Republicans see an opening.

Dr. Steve Ferrara is already running for the GOP nomination, and national Republicans believe he is a strong candidate. Ferrara is a retired Navy captain who served as a doctor. He volunteered for the Navy during the Gulf War and deployed to Afghanistan in 2009.

Ferrara worked in Congress when he returned home as a National Academy of Sciences fellow. He then became the chief medical officer for the Navy. Between May 21 and July 30 Ferrara raised more than $256,000, according to Federal Election Commission documents. He has $245,000 in cash on hand.

Dave Giles, the 2016 nominee, is running again in the 9th District. He lost to Sinema by 22 points and faced questions about spending campaign funds on personal items.

With Sinema running for Senate, Phoenix Mayor Greg Stanton is expected to jump in the race on the Democratic side. 

Stanton’s second term as mayor ends in 2019, and term limits prevent him from running again. In 2015 he was elected to a second term with 65 percent of the vote.

Stanton has been critical of President Donald Trump, writing an op-ed in the Washington Post urging Trump to delay his campaign rally in Phoenix following the violence in Charlottesville, Virginia.  Stanton also recently donated $10,000 from his state campaign account (which he cannot transfer to a congressional campaign) to assist undocumented immigrants brought to the country as children who are renewing their enrollment in the Deferred Action for Childhood Arrivals program.

Former House Minority Leader Chad Campbell had also been considering a run for the seat, according to two sources with knowledge of the race. Campbell was term-limited in the state House after serving four terms. But one source doubted Campbell would run against Stanton.

Biologist Talia Fuentes was already in the Democratic primary, challenging Sinema because of her centrist voting record. Fuentes ran unsuccessfully in the open 5th District in 2016, losing to Republican Andy Biggs by 28 points. 

“I ran in 5 in 2016 because my family had no one to vote for and that is where I grew up,” Fuentes wrote in a Facebook comment about her candidacy. “Kyrsten Sinema has one of the highest Trump scores of any Democrat in Congress … Time someone held her accountable.”