AMNA NAWAZ: While Republicans are focusing on a crowded presidential field, Democrats are facing a new challenge to their majority in the Senate.

Democratic Senator from West Virginia Joe Manchin announced today that he will not be seeking reelection next year, raising the stakes in the Democrats' battle to maintaining power in the Upper Chamber.

Lisa Desjardins is here with me in the studio for more.

Lisa, good to see you.

LISA DESJARDINS: Hi.

AMNA NAWAZ: So what do we know?

Why is Manchin leaving the Senate now?

LISA DESJARDINS: Well, Manchin sent out a video statement today.

And in that, he said this was one of his hardest decisions of his life, but that, in his heart of hearts, in his quotes, he feels that he has done what he came to do for West Virginia, and it essentially is time for him to leave.

Now, as you say, this is an issue for Democrats potentially.

He's 76 years old, and he is the last statewide elected Democrat in the state of Virginia, a Kennedy Democrat.

That's sort of been part of his political identity is the kind of Kennedy era.

And now they have to figure out, can anyone, any other Democrat win that seat?

Joe Manchin himself, of course, didn't -- almost didn't win last time.

He just won by three points.

AMNA NAWAZ: Well, his announcement, for those who listen to it, didn't exactly sound like a goodbye.

He's been asked previously, too, if he would run for president.

He didn't rule it out.

Do we know?

Is he running?

LISA DESJARDINS: Right.

I think that part of the calculus here is he would have a challenging time trying to become a senator.

My sources close to Senator Manchin tell me that he's opening the door, let's say, to a presidential run.

He plans on traveling around the country.

And here's what he said in his video today.

SEN. JOE MANCHIN (D-WV): I will not be running for reelection to United States Senate, but what I will be doing is traveling the country and speaking out to see if there is an interest in creating a movement to mobilize the middle and bring Americans together.

LISA DESJARDINS: A movement to mobilize the middle or potentially nominate Joe Manchin as an independent candidate for president.

This is not yet a presidential run, but it is some sort of exploration.

There is also a real question here, I think, for Joe Manchin.

Are there centrists in this country anymore?

Is there a viable political momentum that can be galvanized for moderates, for centrists?

He's not the only centrist trying to do this.

He's a Democrat.

And we're going to see his schedule coming up.

We will see exactly where he thinks the middle of the country lives.

AMNA NAWAZ: One to watch, for sure.

The meantime, what does it mean for the balance of power in the Senate and for the fight ahead in 2024?

LISA DESJARDINS: Lots of discussion about this today around Washington and around the entire country.

So let's just start by explaining -- reminding viewers that, right now, our U.S. Senate has 51 Democrats and 49 Republicans.

So let's say Manchin's seat, as it is expected now, goes Republican, 50/50.

So let's look at the rest of the map for next year's Senate elections.

We have got 34 seats up for grabs.

And if you look at this map, you can see there aren't a lot of -- there are several Democratic seats that are going to be tough.

Montana, light blue, that's Jon Tester.

That might be tough to hold.

Look at that yellow seat.

That's Kyrsten Sinema in Arizona and also yellow in Ohio.

That's Sherrod Brown.

Those are three seats.

Democrats have to run the table basically to keep all three of those seats.

And a reminder, Kyrsten Sinema is no longer a Democrat.

She's an independent.

There's another Democrat trying to run for that seat.

All of this is to say it is even more uphill now for Democrats to keep control of the Senate.

Not impossible, but this makes it harder.

AMNA NAWAZ: Lisa Desjardins covering it all, thank you so much.

LISA DESJARDINS: You're welcome.