Phoenix Mayor Greg Stanton will soon leave his post as the leader of the nation's fifth-largest city to run for Congress.

In a video announcement Thursday, Stanton declared his candidacy for the congressional seat currently held by Rep. Kyrsten Sinema, D-Phoenix, who is challenging Republican Sen. Jeff Flake.

Stanton began his announcement by saying, "There are many miles between Phoenix and Washington, D.C., but what separates us most is how we work to solve problems."

He listed a series of what he sees as his accomplishments as mayor, noting that he accomplished all of them with "real bipartisan support — Republicans and Democrats actually working together."

"With new leadership we can remind Congress about what it's supposed to do get together and solve problems to make people's lives better just like we do in Phoenix," he said.

Congressional District 9 is considered a swing district, though Sinema, a moderate Democrat, won in each election since the district was established following the 2010 census.

The district contains most of Tempe and parts of Chandler, Scottsdale, Mesa, Ahwatukee and north Phoenix.

Stanton is an attorney and formerly served as the state's deputy attorney general. He served on the Phoenix City Council for nine years before he was elected mayor in 2011.

During his political career, Stanton has focused on downtown development, public transportation and social issues. He's also been quick to insert himself into national conversations about immigration and health care. He's a vocal critic of President Donald Trump, even publicly asking him not to visit Phoenix in August.

There was plenty of speculation that Stanton, a prominent Democrat in his seventh year as Phoenix mayor, would leave his second term — which ends in 2019 — early to seek a national or statewide office.

Stanton will have to resign from his mayoral post, but not until he submits his election petitions. Those are due May 30, though he could choose to leave sooner to devote greater attention to the congressional race.

Stanton, who has more than $500,000 in leftover campaign funds from his prior races, will not be able to use any of that money in this federal election, according to campaign laws.

Last month he donated $10,000 toward DACA renewals. He has not said what he intends to do with the remainder of the campaign fund.

If Stanton resigns, the council will choose one member to serve as interim mayor until the city can hold a special election. The interim mayor will represent his or her district and the city as a whole simultaneously.

That election could be held in March, May, August or November depending on the date of Stanton's resignation. The sooner he resigns, the sooner the city can call for an election.

Stanton's departure would likely trigger multiple other Phoenix elections as well.

Within 10 days of Stanton's leaving, anyone interested in running for his seat must declare.

If any mayoral candidates are current council members — a likely scenario — they would also have to resign from their seats, which means a special election must be held to fill those vacancies.

The remaining council members will call for applicants interested int the open council seats and select temporary replacements until new members are elected.