Stay Updated on Developing Stories

Senate Democrats just got a huge boost in their push for the majority

(CNN) Former Montana Gov. Steve Bullock's decision to reverse course and run for the Senate this November is a massive recruiting coup for Democrats that not only makes the party competitive in that state but also improves their odds of retaking the majority this fall.

Bullock, who left office last year as a popular two-term governor, is widely regarded as the only Democrat with a credible chance of beating freshman Republican Sen. Steve Daines in a state that tends to favor Republicans at the federal level. (Bullock, who ran briefly for president in this election, had repeatedly insisted that he had no interest in the Senate. He has apparently changed his mind.)

A Bullock run, which he is expected to announce sometime before Monday's filing deadline, will have reverberations well beyond the Last Best Place.

A reminder of the majority math for Democrats makes clear why. To retake the majority, Democrats need to net three seats if their side wins the White House and four if they don't.

Before Bullock's decision, non-partisan handicappers -- like the Cook Political Report -- rated three GOP seats as deeply imperiled: Arizona Sen. Martha McSally, Colorado Sen. Cory Gardner and Maine Sen. Susan Collins. But Democrats also have to defend Sen. Doug Jones (D) in GOP-friendly Alabama, a prospect that got much harder when uber-controversial Roy Moore didn't make the GOP runoff earlier this week.

While Bullock is no sure thing -- Daines had $5 million in the bank at the end of 2019 -- his candidacy absolutely makes the race competitive. Put another way, it gives Democrats a bit more margin for error in their majority push. In addition to the trio of endangered GOP incumbents, Montana now joins a second group of GOP-held seats where Democrats expect to have a real chance, which includes: Georgia Sen. Kelly Loeffler, North Carolina Sen. Thom Tillis and the open Kansas seat.

For Democrats to ensure they take back the majority then, the two obvious scenarios are:

1) Get Jones reelected, sweep the three most endangered GOP seats and win one of Montana, Georgia, North Carolina or Kansas

2) Jones loses, meaning Democrats need to win five Republican seats from Arizona, Colorado, Maine, Montana, Georgia, North Carolina or Kansas.

Adding another seat to that mix -- and one that was simply off the board without Bullock -- allows Democrats some leeway to lose, say, in Georgia, and not have their chances at the majority disappear.

To be clear: Bullock running boosts Democratic chances. But it does not make the majority a sure thing. Not even close. Given the landscape of states where Democrats need to win in order to retake the majority, it's still significantly less than a 50-50 proposition.

Outbrain