Republican U.S. Senate candidate Martha McSally has conceded the Arizona race to Democrat Kyrsten Sinema.

In a video posted on Twitter, McSally wished Sinema "all success," in her new role in Congress and said she is "grateful to all those who supported me in this journey."

"As I traveled around this state, I was so inspired by the many people that I met and I am convinced Arizona is the best state in the country," McSally said. "And our best days are still yet to come and I'm going to continue to pray for our success. Thank you so much."

Later, in a letter to her supporters, the Air Force veteran wrote, "It was an honor to have you all as my wingmen and wing women in this mission. We came up short, but we gave it all we had and I am proud of you all and grateful for you."

Sinema started her remarks with thanks to veterans, including her brothers and McSally.

“We launched this campaign because Arizona veterans and all everyday Arizonans deserve a leader who will fight for them in the United States Senate," she said.

As of Sunday, there were still 200,000 votes that had yet to be counted, which stems from Arizona’s practice of allowing voters to mail in ballots up until and through Election Day. Those ballots then have to be verified based on the signature on the outside of the ballot.

The battle to fill the seat left open by outgoing Republican Sen. Jeff Flake led to a close race between two sitting congresswomen. McSally started out with a slight lead, but as more and more votes have been counted, Sinema had taken over and was widening her edge.

Republicans hoped to hold onto Flake's seat by nominating McSally, who served as the first female fighter pilot to fly in combat, but faced a strong challenge from Sinema, who regularly had a slight edge in national polls leading up to Election Day.

Nicole Neri/Reuters

Regardless of the tight nature of the race and the party power implications that came with it, the outcome was bound to be historic as the leading candidates were both women in a state that has never had a female U.S. senator before.

That said, both McSally and Sinema are current members of Congress, representing an urban and a border district respectively.

Matt York/AP

Republicans were not subtle in their desire to hold on to the seat, with a string of high-profile party members — including President Donald Trump, former President George W. Bush, former Gov. Mitt Romney, Donald Trump Jr. and Sens. Susan Collins, Lindsey Graham and Jon Kyl — campaigning on behalf of McSally.

McSally closed out her campaign at a Republican election eve rally in Prescott, where Sen. John McCain’s widow Cindy McCain made a rare public appearance. Though she didn’t directly endorse McSally, she did call on Arizonans to work together “win or lose.”

Sinema focused less on tying her campaign to the larger Democratic party, rarely mentioning her party affiliation in her campaign ads and instead describing herself as an independent.

Democrats were optimistic about their chances to turn the state from red to purple, hoping that changing demographics in the state and potential distaste of the Trump administration could help catapult Sinema to victory.

Preliminary exit poll results suggested that health care was a huge issue for Arizona voters, with 41 percent saying that it was the most important topic to them, squeezing out ahead of immigration, which 32 percent of Arizonans said was their top issue.

Both topics were major points of discussion on the campaign trail. Sinema said that access to affordable health care was a topic that frequently came up when she spoke with voters, and that became a difficult point for McSally who had to defend her vote, which was in line with the Trump administration, in support of the proposed Republican repeal of Obamacare.

Arizonans were among some of the first in the country to start casting ballots, with early voting starting in the Grand Canyon state on Oct. 10. And that didn’t stop voters from turning out on Election Day.

“This election is looking more like a presidential election in the amount of ballots,” Maricopa County Recorder Adrian Fontes said on Election Day.