Washington (CNN)Florida Gov. Rick Scott shook up the Senate map Monday with his decision to challenge Democratic Sen. Bill Nelson.
Senate Key Race alerts: Florida now a Toss-Up while Tennessee is Lean Republican
Scott's entrance ends months of will-he-or-won't he speculation and brings a sigh of relief for Republicans, who had lacked a credible opponent for Nelson.
The Sunshine State contest is likely to be one of the most expensive in the country this year, making Scott's net worth of nearly $150 million an added benefit of his candidacy for Republicans. The Republican governor has shown a willingness to dip into his personal funds in previous races.
If Democrats are to have any hope of reclaiming the Senate majority they will need to hold onto Florida -- and most, if not all, of the other nine states with Democratic incumbents that Trump won in 2016. Republicans currently hold a 51-49 advantage in the Senate, meaning Democrats need a net gain of two seats.
Nelson, who is seeking a fourth six-year term in the Senate, started the calendar year with $8 million in the bank. He won his most recent race in 2012 by 13 points over Republican Connie Mack IV while at the same time Barack Obama carried the state by just a single point over Mitt Romney.
In 2016, Donald Trump defeated Hillary Clinton by two points in the state.
For his part, Scott is no stranger to close races, having won a pair of roughly single-point contests in 2010 and 2014.
A Quinnipiac University poll released in late February showed Nelson edging out Scott by four points, 46% to 42% in a hypothetical race, thanks in part to a 13-point advantage among independents.
Given its importance not just to the Senate math, but presidential politics, Florida is sure to be one of the marquee races of 2018.
It moves from Lean Democratic to Toss-Up in our rankings.
At the same time, we are moving the Tennessee Senate contest in the direction of the Democrats.
The primary in the Volunteer State isn't until August, but former Democratic Gov. Phil Bredesen and GOP Rep. Marsha Blackburn already are locked in a general election battle.
A recent poll from Middle Tennessee State University showed Bredesen up 10 points on Blackburn, 45% to 35%, driven in part by the 20% support the Democrat received from Republican respondents.
Even if the margin is closer than that, a single-digit race in favor of either candidate in a state Trump claimed by 26 points means it is worth watching.
All of which helps explain why in his first television ad Bredesen declared, "I'm not running against Donald Trump. I'm running for a Senate seat to represent the people of Tennessee."
Bredesen, who served two terms as governor from 2003 to 2011, is getting some outside help from former Vice President Joe Biden, who will visit Nashville this week to attend a fundraiser for the Democrat.
We'll have to wait until July to see how much the Biden event helped stock Bredesen's coffers, but first quarter fundraising numbers are set to be published in the coming days and will offer another sign of the state of play in Tennessee.
Another factor worth tracking is any intraparty GOP drama as the senator Blackburn is hoping to replace -- Bob Corker -- played coy about a possible endorsement of his fellow Republican.
But on Thursday Corker tweeted he was "sending a contribution" to Blackburn's campaign "and wish her well in her race for the U.S. Senate."
This race moves from Likely Republican to Lean Republican.
We have also updated the seat vacated by retired Sen. Thad Cochran to include Sen. Cindy Hyde-Smith, who was sworn in on Monday. She will run as the incumbent for her seat in a nonpartisan election in November. CNN still ranks the race as "Safe Republican," though Hyde-Smith will face a challenge from Republican State Senator Chris McDaniel, along with Democrats seeking another win in the South. A runoff between the top two finishers will be held at the end of the November if no candidate wins at least 50% of the vote, which is widely expected given the amount of candidates currently in the race.
This story has been updated.