Arizona GOP Rep. Martha McSally (AZ-02) uncorked one of the worst kept secrets of 2018 by announcing her bid for Senate today. Over her two terms, McSally has cultivated a popular profile as a trailblazing fighter pilot and moderate Republican who fought for Pentagon funding for Tucson's A-10 Warthog. It allowed her to win reelection with 57 percent in 2016 while Hillary Clinton carried the district 49 percent to 44 percent.

But without McSally, Republicans may struggle to hold this district. In fact, Democrats are hoping for a scenario in which McSally loses the GOP Senate nomination to a more conservative candidate and moderate Republicans abandon the ticket altogether, allowing Democrats to waltz into this middle-of-the-road seat.

McSally's votes for the Republican health care and tax bills had already made her the target of Democratic attacks, and it makes sense that McSally is running for Senate: President Trump lost the 2nd CD, but won statewide in 2016. Some Republicans are optimistic Tucson Hispanic Chamber of Commerce President Lea Marquez-Peterson has the right profile to keep the seat in GOP hands, but she almost certainly won't have the primary field to herself.

Meanwhile, the Democratic frontrunner is former 1st CD Rep. Ann Kirkpatrick, who moved from Northern Arizona to Tucson following her losing challenge to Sen. John McCain in 2016. Kirkpatrick is running as an unabashed progressive and has the support of former Rep. Gabrielle Giffords and Mark Kelly. She'll also seek to deflect the carpetbagger label by talking about moving to Tucson to care for two grandchildren who were born prematurely.

Kirkpatrick won't have a free ride in the August primary: 2016 nominee Matt Heinz is probably her most serious competition, but former Assistant Army Secretary Mary Matiella and hotel manager Billy Kovacs are running too. However, Giffords's endorsement of Kirkpatrick will be difficult for others to overcome. And, the money she spent in the Tucson market while running for Senate helps give her an initial name recognition advantage.

If Kirkpatrick does make it to the general, Republicans will surely paint her as too far left for Tucson. But here's a statistic that should worry Republicans: in the past three midterm elections, in situations where an incumbent has vacated a district that voted for the opposite party in the most recent presidential election, the incumbent's party has batted zero percent (0/10) attempting to hold the seat.

If this were a neutral national environment, this open seat would be a Toss Up. But with President Trump's approval hovering in the 40 percent range, this race moves to the Lean Democratic column.