By Alex Rogers and Clare Foran, CNN

(CNN) -- Massive fundraising in Maine. A countdown clock in Alabama. Calls and texts encouraging potential challengers in Colorado. Just a few weeks after 2018's Election Day, the signs are clear: the 2020 Senate campaigns are already underway.

Democrats start 2020 in a solid position, though they remain in the minority in the upper chamber of Congress. Of the 12 Democratic seats up for re-election, only two are from states President Donald Trump won in 2016 -- Alabama's Doug Jones and Michigan's Gary Peters. Republicans have more seats to defend, with 22 GOP seats on the line.

"The map looks good for the Democrats — I'll tell you that," Sen. Catherine Cortez Masto, the new chair of the Democratic Senatorial Campaign Committee, told CNN.

Democrats will have opportunities to flip seats and potentially win back the majority in 2020. But the party could face difficult races against Republican incumbents in purple states like Maine and Colorado. Democrats will also have to defend the most vulnerable seat currently on the map in the deep red state of Alabama.

Republicans optimistic in Alabama

Jones hopes that his campaign playbook of running on health care, against tariffs and carefully explaining his vote against Judge Brett Kavanaugh will allow him to save his seat.

But Republicans are confident they can take it back, presuming they put up a significantly stronger candidate than Jones' last opponent, Roy Moore, who lost by only a point and a half despite facing accusations of sexual assault, which he denied. Even before the 2018 midterms were over, the Alabama Republican Party was counting down the days on its website until Jones "is unseated" in the 2020 contest.

One question looming over the race is whether Jeff Sessions, who formerly held the Senate seat, decides to run after President Donald Trump fired him as attorney general. If Sessions shows signs of entering the race, that would change the political calculus for other Republicans considering a bid.

So far, at least one potential GOP challenger is publicly weighing the possibility of a run against Jones: Rep. Bradley Byrne of Alabama.

Seth Morrow, a spokesman for the congressman, told CNN that Byrne has "made clear he is interested in running," but isn't expecting to reach a final decision "until next spring at the earliest."

Some in the state seem to think Byrne's mind is already made up. "He's running," Jonathan Gray, an Alabama Republican strategist, said in an interview. "Has Bradley announced? Not publicly. But the conversations are happening."

Supporters have encouraged Rep. Mo Brooks to run for Senate again after he ran in the 2017 Republican primary, but the congressman has told Byrne that at this time it is "unlikely" he will run in 2020, an Alabama Republican close to congressman Brooks told CNN.

When asked if he would run again, Brooks told CNN, "Bradley Byrne looks like he's running — talk to him."

Democrats look for pickups

With so many seats to defend, Republicans could defeat Jones and still lose the Senate. But it would be a tough slog for Democrats, who would then need to gain even more seats to win a majority, perhaps by winning the open seat left by the retiring Arizona Sen. Jon Kyl or by defeating incumbent senators like Thom Tillis of North Carolina, Cory Gardner of Colorado and Susan Collins of Maine.

For now, they're jockeying for the opportunity. In North Carolina, "the name people talk about most" is state Sen. Jeff Jackson, according to Gary Pearce, a longtime strategist in the state, who added that others, including a woman or someone of color, may also emerge.

In Arizona, Grant Woods, the former state Attorney General and former chief of staff to the late Sen. John McCain, former astronaut Mark Kelly, the husband of former Rep. Gabby Giffords, Rep. Ruben Gallego and Greg Stanton, the former Phoenix mayor who was elected to the House in the 2018 midterms, are on the list of potential candidates Democratic strategists have mentioned.

In Colorado, Crisanta Duran, the Democratic House speaker of the state's House of Representatives and Mike Johnston, a former state senator who ran in the Democratic gubernatorial primary in 2018, both told CNN they are considering a 2020 Senate run.

"I have had a great number of folks reach out to me and ask me if I would consider running," Johnston said. "There has been a big increase in phone calls and text messages since election night."

Crowdfunding campaign draws attention to Maine

In Maine, Democrats are hoping to sweep out of office Collins, who will be the only Republican in New England's 33-person congressional delegation in the next Congress. In the past year, she has infuriated both liberals and conservatives alike with her votes to send Kavanaugh to the Supreme Court and save the Affordable Care Act from repeal.

In the aftermath of the Kavanaugh vote, one crowdfunding campaign has raised nearly $4 million to support a future challenger to Collins.

"I think that has piqued a lot of people's interest," Toby McGrath, a political strategist in Maine who ran both of Barack Obama's presidential campaigns in the state, said of the crowdfunding efforts. "I think a lot of people will be thinking about running."

Even Democrats in the state privately acknowledge, however, that Collins won't be easy to defeat. The Maine Republican has successfully won election to the Senate four times already and has frequently won by wide margins. Jared Golden, a Democrat who just flipped a Republican seat in rural Maine, touted in his advertisements that he worked as an aide to Collins.

"Overall, her votes have reflected pretty squarely what her constituency is looking for," said Lance Dutson, a strategist who worked on previous Collins campaigns. "And when it comes down to making these tough, 50-50 calls, I think she does what she thinks is right and then moves forward from it."

But should Collins decide to run for re-election, she will likely face a tough environment with national interest in her race.

A number of names have been floated as potential Democratic challengers to Collins.

Sara Gideon, the Democratic speaker of the Maine House of Representatives, is "seriously considering" running, according to spokeswoman Mary-Erin Casale.

Other names that have been talked about as potential challengers are Rep. Chellie Pingree, who unsuccessfully challenged Collins in a 2002 Senate race, and Susan Rice, who served as national security adviser in the Obama administration and fueled speculation that she might enter the race after she tweeted "me" last month in response to a tweet asking who would run for the Senate seat. Rice later said that she was "not making any announcements," but she has continued to weigh in on Twitter with commentary on Collins.

Other senators to keep an eye on

While they'd likely not change control of the Senate, there are a number of other senators whose loss would change the makeup of the chamber. First-term senator John Kennedy of Louisiana, for example, is considering a run for governor.

"I think Gov. (John Bel) Edwards is taking our state in the wrong direction, and I think based on the extensive polling that I've done and I've seen there are only two people who can beat him: one is Scalise and one is me," Kennedy told CNN, referring to House Republican Whip Steve Scalise, who has rejected any interest in running for governor.

"I haven't made a decision," Kennedy added. "I've enjoyed being in the Senate."

There are also rumors of retirements surrounding some members who have roamed the halls of the Capitol for decades.

The Cook Political Report notes that seven Republicans will be 70 or older at the time of the 2020 elections: Sen. David Perdue of Georgia, Sen. Michael Enzi of Wyoming, Sen. Mitch McConnell of Kentucky, Sen. James Risch of Idaho, Sen. Lamar Alexander of Tennessee, Sen. Pat Roberts of Kansas and Sen. James Inhofe of Oklahoma.

Unlike McConnell, who has already made moves to run for reelection, two of the oldest senators — Roberts and Inhofe — have not said whether they'd go for another six-year term.

"The first order of business" for Roberts is "finishing the farm bill" that is "critical to our (agriculture) economy, according to spokeswoman Sarah Little. "With the ink on the 2018 election cycle barely dry, Senator Roberts would like to give Kansans a breather before the campaigning starts all over again."

Yet at least one member of Congress would consider running if Roberts, a fourth-generation Kansan, decided to retire after serving in the House and Senate for nearly 40 years. In interviews, Kansas political strategists note that Rep. Roger Marshall would be well-positioned to take over from Roberts should he decide to retire. Former Sen. Bob Dole, as well as current senators Roberts and Jerry Moran, all represented the massive first congressional district that Marshall now serves in the House.

Marshall, an obstetrician-gynecologist who has delivered more than 5,000 babies, told CNN that he and his wife "would talk seriously about" running if Roberts, 82, retired. Marshall added that he would "never, ever" run against the senator, that he doesn't see Roberts retiring in the "near future," that Roberts is doing a "great job" especially with the Farm Bill and that he considers the senator a mentor.

"I'll cross that bridge when we get to it," said Marshall. "I think Senator Roberts is not going anywhere. I just can't emphasize enough that we're fully supportive of him."

As for Inhofe, 84, he told CNN he's "not necessarily" going to run again.

"Last time I ran, all they could say is 'Inhofe you're too old to be in the United States Senate,'" said Inhofe. "My response was, when I'm too old to fly airplanes upside down, then I'm too old to fly in the United States Senate."

Inhofe noted that he still flies upside down.

"That's right — I qualify," he said. "I have not made any plans to leave."