Washington (CNN) Democrats have a chance to parlay their base's anti-Donald Trump energy into victories -- and chip into the 24 GOP seats they need to retake the House majority -- in a set of five upcoming special elections.

Four of those seats were vacated by Republicans picked by Trump for Cabinet posts. Democrats' hopes are highest for a closely-watched race in Georgia -- and the party is keeping its eyes on Montana, too. Republicans, meanwhile, are confident they'll hold onto districts in Kansas and South Carolina.

The lone Democratic-held seat is up in California -- and is all but sure to remain in Democratic hands.

Here's a look at the five special elections set for this spring -- ordered from most to least likely to change hands:

1. Georgia's 6th District

Why it's open: Former Rep. Tom Price was selected as President Donald Trump's secretary of Health and Human Services

Special election date: April 18 with a runoff June 20

2016 House results: Price - 62%, Democrat Rodney Stooksbury - 38%

2016 Presidential results: Trump - 48%, Clinton - 47%

2012 Presidential results: Romney - 61%, Obama - 38%

Two numbers tell the story of the hyper-competitive race in Atlanta's northern suburbs: The 22-point swing in presidential results in Democrats' favor in just a four-year span, and the $3 million-plus that Democratic candidate Jon Ossoff, a 30-year-old former House staffer and documentary filmmaker, has already raised, with a major assist from liberal blog DailyKos.com.

The fractured Republican field currently features 11 candidates. The GOP's hope: It can hold Ossoff below 50% in the April 18 "jungle primary" so that the top two candidates -- Ossoff and, likely, one Republican -- advance to a June 20 run-off where the GOP expects the district's historically conservative bent (this was, after all, Newt Gingrich's seat) to hold up.

The race has become a cause celebre for the anti-Trump resistance, and both parties are noticing: Already, the Congressional Leadership Fund super PAC has pumped $2.2 million into ads attacking Ossoff as inexperienced and unserious. And the Democratic Congressional Campaign Committee has already pumped resources into staffing on the ground.

Former Georgia secretary of state Karen Handel leads the way among Republican candidates, with Bob Gray, Judson Hill and Dan Moody also in the running.

Moody got a big boost when Sen. David Perdue endorsed him in a 30-second TV spot, declaring the former state representative and businessman "one of us" who "cares more about getting results than getting credit."

Handel, meanwhile, faces opposition from the conservative Club for Growth, attacking her spending as secretary of state and Fulton County commissioner and labeling her a "big-spending, career politician we can't trust with our money."

2. Montana's at-large House seat

Why it's open: Former Rep. Ryan Zinke became Trump's secretary of the Interior Department

Special election date: May 25

2016 House results: Zinke - 56%, Democrat - Denise Juneau 41%

2016 Presidential results: Trump - 57%, Clinton - 36%

2012 Presidential results: Romney - 55%, Obama - 42%

Democrats have won Senate and governor's races in Montana -- but they haven't managed to snag the state's lone House seat in almost 20 years.

Banjo-playing populist Rob Quist hopes to change the party's fortunes against Republican Greg Gianforte, a software entrepreneur who lost 2016's governor's race to Democrat Steve Bullock.

Republicans are much more confident in their chances of holding Montana's seat than they are in Georgia -- and Trump's populist appeal could help insulate the party in a state where he bested Romney's results.

3. Kansas' 4th District

Why it's open: Former Rep. Mike Pompeo was chosen as Trump's CIA director

Special election date: April 11

2016 House results: Pompeo - 61%, Democrat Daniel Giroux - 30%

2016 Presidential results: Trump - 60%, Clinton - 33%

2012 Presidential results: Romney - 62%, Obama - 36%

In terms of competitiveness, it's a steep drop from Montana to western Kansas -- where this reliably red district is expected to stay that way.

One way you know Democrat James Thompson faces long odds against Republican Ron Estes here: He's quibbling with the state Democratic Party over its rejection of his request for $20,000 for mailers.

But the race has taken shape more quickly than a similar contest in South Carolina, and Democrats' hopes are that anti-Trump enthusiasm might make for a surprise in a low-turnout affair.

4. South Carolina's 5th District

Why it's open: Former Rep. Mick Mulvaney, a House Freedom Caucus mainstay, was tapped as Trump's budget director

Special election date: June 20

2016 House results: Mulvaney - 59%, Democrat Fran Person - 39%

2016 Presidential results: Trump - 57%, Clinton - 39%

2012 Presidential results: Romney - 55%, Obama - 44%

Fifteen candidates, including three Democrats and seven Republicans, filed for a race in reliably red northern South Carolina. The primaries there are set for May 2, with the winners squaring off in a June contest that could become much more interesting if Democrats have managed to pull off stunners in either Montana or Kansas by then.

5. California's 34th District

Why it's open: Former Rep. Xavier Becerra was appointed California attorney general

Special election date: June 6

2016 House results: Becerra - 77%, Democrat Adrienne Nicole Edwards 23% (no Republican advanced to the general election through the state's jungle primary)

2016 Presidential results: Clinton - 84%, Trump - 11%

2012 Presidential results: Obama - 83%, Romney - 14%

Becerra's departure cost House Democrats one of their leading voices -- but it's almost certain they won't lose the seat.

Of at least 23 candidates so far, 19 are Democrats and just one is a Republican. Among the names worth watching are state assemblyman Jimmy Gomez and Arturo Carmona -- who was Bernie Sanders' deputy political director during the 2016 Democratic presidential primary.