A sad end to Isakson’s political career and a minor, possibly major, disaster for the GOP in the making.

Republican U.S. Sen. Johnny Isakson said Wednesday he was stepping down from the U.S. Senate at the end of 2019 as he struggles with Parkinson’s disease, leaving a vacancy that Gov. Brian Kemp will soon fill.

A four-decade veteran of Georgia politics, Isakson has served in the U.S. Senate since 2005. He won his third term in 2016 by a comfortable margin and isn’t up for re-election until 2022.

Isakson, 74, has suffered several falls since announcing he has Parkinson’s, which limits his balance and mobility. He recently spent six days in an inpatient rehabilitation program at Marietta’s WellStar Kennestone Hospital after being hospitalized in Washington on July 16.

Isakson easily won all three of his Senate elections in Georgia, a state that’s become more purple during his tenure. In 2016 he actually ran ahead of Trump there, defeating his Democratic opponent 55/41 while Trump held off Clinton 50/45. Until this morning the GOP didn’t need to worry about defending his seat until 2022. Now, suddenly, they have not one but two Senate races on their hands in Georgia in 2020. David Perdue is running for reelection to another six-year term, remember. And Georgia law requires that any Senate vacancy be filled for the remainder of the vacant term by the winner of a special election held during the next regularly-scheduled election. That’s next year, of course.

Which is a long way of saying that if the economy slides and Trump’s numbers start to sink, Democrats would stand a real (if outside) chance of picking up two Senate seats in “red” Georgia. If you’re looking for scenarios in which the Senate might flip, you’ve now got one. Two seats in Georgia, a Mark Kelly win in Arizona, bad days for Susan Collins and Cory Gardner in the battleground states of Maine and Colorado and suddenly not even ousting Doug Jones in Alabama would be enough for Republicans to hold onto a majority.

Imagine President Warren with total control of government. The filibuster will be dead within five minutes after the new Democratic Senate is sworn in.

Seth Mandel asks the obvious question:

Schumer pleaded with Abrams to challenge David Perdue but she declined, knowing that it would be hard to defeat a reasonably popular incumbent and that two losses in the span of two years might damage her “rising star” luster. But she wouldn’t need to challenge a real incumbent for Isakson’s seat, merely the temporary appointee named by Kemp. I’m not sure she can say no to Democrats now that they’ve got a shot at winning two seats. If she really is the strongest hand they can play, imagine how they’ll resent her if she sits out the election and they lose one or both races narrowly.

As for who Kemp might appoint, he could always choose himself but that would create a vacancy in the governor’s seat, and Abrams probably would take a run at that. Plus, having only barely defeated her for his current office, it’s not clear that Kemp would be the GOP’s strongest play at holding Isakson’s Senate seat. Ideally he’d want to name someone with high name recognition and who’s young enough to run for a full term in 2022. Former Gov. Nathan Deal is probably too old at 77. Newt Gingrich is 76, and likely too divisive to be considered the GOP’s best chance. Kemp could put aside the bitterness of last year’s gubernatorial primary by nominating his Republican opponent in that race, Casey Cagle, who’s just 53. But if he does that, he might end up barring his own path to the Senate eventually: Someone as old as Perdue might serve only one term, vacating the seat for the 2028 election, whereas Cagle could serve for decades with the benefit of incumbency, making him primary-proof.

A better option is Sonny Perdue (cousin of David), who served two terms as governor and is currently serving as Trump’s secretary of agriculture. He’s 72, which is plenty young enough for the Senate. And if he ran, the GOP would have a straightforward mnemonic pitch to Georgians next fall: “Look for the Perdue name on both ballots.” I’d bet on a Sonny Perdue/Abrams race.

Update: She’s gonna make enemies in her party if she sticks to this.