Democratic enthusiasm is creating crowded primary fields in some GOP-held districts.

That energy could help Democrats win the 24 seats they need to flip control of the House. But all the enthusiasm comes with its disadvantages: Democrats will need to spend time and resources before they can take on the GOP incumbents.

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Here are seven Republican-held districts that are already seeing a groundswell of interest from Democrats:

Virginia’s 10th District Rep. Barbara Comstock

Comstock’s Northern Virginia swing district right outside Washington, D.C., has been a top Democratic target. Democratic presidential nominee Hillary Clinton Hillary Diane Rodham ClintonHillicon Valley: FBI chief says Russia is trying to interfere in election to undermine Biden | Treasury Dept. sanctions Iranian government-backed hackers The Hill's Campaign Report: Arizona shifts towards Biden | Biden prepares for drive-in town hall | New Biden ad targets Latino voters FBI chief says Russia is trying to interfere in election to undermine Biden MORE beat now-President Trump in the district by 10 points, but Democrats fell short down the ballot when Comstock won reelection by just about 6 points.

Democrats are coming out in droves to unseat Comstock. Army veteran Daniel Helmer, who served in Iraq and Afghanistan, raised $120,000 and has already toured businesses across the district.

Other declared Democrats include former Obama official Lindsey Davis Stover and Kimberly Adams, former president of a local teachers union. And Dorothy McAuliffe, the wife of outgoing Gov. Terry McAuliffe (D), is considering a bid.

LuAnn Bennett, the 2016 Democratic nominee who lost to Comstock, told the Loudoun Tribune she doesn’t plan to run.

But perhaps the biggest name to enter the race is state Sen. Jennifer Wexton, who was courted by the Democratic Congressional Campaign Committee (DCCC). She’s a former county prosecutor who has experience winning competitive races.

Wexton’s entry prompted election handicapper Cook Political Report to move the race from lean Republican to a toss-up.

California’s 45th District Rep. Mimi Walters

Walters hasn’t always been a Democratic target, but she has weathered attacks for voting to advance the House GOP’s unpopular bill to repeal and replace ObamaCare out of committee.

Now she’s been singled out as a top California target in a district Clinton won by more than 5 points.

Consumer advocate and former Wall Street watchdog Katie Porter entered the race with high-profile endorsements from Sens. Elizabeth Warren Elizabeth WarrenWarren, Schumer introduce plan for next president to cancel ,000 in student debt The Hill's 12:30 Report - Presented by Facebook - Don't expect a government check anytime soon No new taxes for the ultra rich — fix bad tax policy instead MORE (D-Mass.) and Kamala Harris (D-Calif.). She was a former law student of Warren’s, and the two have worked together.

Porter isn’t the only professor from the University of California, Irvine looking to unseat Walters. Dave Min is a law professor who served as a former economic policy adviser to Senate Minority Leader Charles Schumer Chuck SchumerMcConnell accuses Democrats of sowing division by 'downplaying progress' on election security Warren, Schumer introduce plan for next president to cancel ,000 in student debt Schumer lashes out at Trump over 'blue states' remark: 'What a disgrace' MORE (D-N.Y.) and at the liberal think tank Center for American Progress. His rollout included local Irvine endorsements.

Kia Hamadanchy, a former aide to Sen. Sherrod Brown Sherrod Campbell BrownEmboldened Democrats haggle over 2021 agenda Hillicon Valley: Russia 'amplifying' concerns around mail-in voting to undermine election | Facebook and Twitter take steps to limit Trump remarks on voting | Facebook to block political ads ahead of election Top Democrats press Trump to sanction Russian individuals over 2020 election interference efforts MORE (D-Ohio), said he raised $100,000 in two weeks. Hamadanchy, who is Iranian-American, said Trump’s travel ban on citizens of Iran and other Muslim-majority countries motivated him to run.

California’s 48th District Rep. Dana Rohrabacher

Rohrabacher has served in Congress for nearly three decades, but his well-known pro-Russia stance is now in the spotlight as Congress and the FBI investigate Russian interference in the U.S. presidential election.

Rohrabacher has already drawn a few Democratic challengers. Democratic margins are closer here than in other targeted districts — Clinton won the district by less than 2 points.

A Democratic attempt to unseat Rohrabacher could be hindered by the Republican pasts of some challengers. Business owner Laura Oatman was a Republican until 2008 and registered independent to vote for former President Barack Obama Barack Hussein ObamaThe Hill's 12:30 Report - Presented by Facebook - Don't expect a government check anytime soon Trump appointees stymie recommendations to boost minority voting: report Obama's first presidential memoir, 'A Promised Land,' set for November release MORE, according to the Orange County Register. She changed her party affiliation to become a Democrat after Trump’s win.

Businessman Henry Rouda is also a former Republican. He said he’s voted for Democratic presidential nominees since 2004 but donated to Republicans until 2007, according to the Register.

The race has also drawn two other Democratic candidates, real estate broker Boyd Roberts and airline pilot Tony Zarkades.

California’s 50th District Rep. Duncan Hunter

Hunter represents a safe red seat that Trump won by 15 points. But the embattled congressman is being investigated by the Justice Department over an alleged campaign finance violation. And he raised eyebrows after using campaign funds to fly a pet rabbit.

That has prompted a long line of Democrats looking to run in the San Diego-area seat.

The DCCC recruited retired Navy SEAL Josh Butner, who currently serves as a local school board member. In his announcement, Butner brought up the allegations that Hunter used campaign dollars on personal expenses.

Ammar Campa-Najjar, a former Department of Labor public information officer, said he was urged to run by people he met while working on Obama’s 2012 campaign, according to the San Diego Union Tribune.

Other Democratic contenders include Grossmont Healthcare District Trustee Gloria Chadwick, Pierre “Pete” Beauregard, a veteran and organic beef rancher, and businessman Patrick Malloy, who lost to Hunter in 2016 by nearly 28 points.

Pennsylvania’s 7th District Rep. Patrick Meehan

Meehan passed on a 2018 Senate bid against Sen. Bob Casey Robert (Bob) Patrick CaseySecond GOP senator to quarantine after exposure to coronavirus GAO report finds brokers offered false info on coverage for pre-existing conditions Catholic group launches .7M campaign against Biden targeting swing-state voters MORE Jr. (D-Pa.). But if he wants to maintain his powerful role on the House Ways and Means Committee, he’ll need to defend a district that Clinton won by more than 2 points.

Three Democrats have announced challenges to Meehan, though they all live outside his suburban Philadelphia district.

Dan Muroff is an attorney and ward leader in Philadelphia, where he currently lives. He was the former president of a gun violence prevention group and worked as an aide to Rep. Jim McGovern (D-Mass.) and former Rep. Joe Hoeffel (D-Pa.).

Muroff unsuccessfully ran in the 2016 Democratic primary for then-Rep. Chaka Fattah’s seat. He said earlier this month he’ll move to the district in a few weeks, according to PoliticsPA.

Molly Sheehan is a biomedical researcher and plans to move back to the district by the end of the year, when she completes her fellowship at the University of Pennsylvania.

Andrew McGinty, an IT consultant who lives in Philadelphia, is also running.

Illinois’ 6th District Rep. Peter Roskam

Democrats are also targeting Roskam’s suburban seat outside of Chicago. Roskam has represented the district since 2007 and easily outperformed Trump, who lost the district by 7 points.

Amanda Howland, a lawyer and psychologist, is looking for a comeback after losing to Roskam by nearly 20 points last year. Former district school board member Suzyn Price also announced a bid.

Local planning commission member Kelly Mazeski, a former state Senate candidate, is looking at a run and met with the DCCC and EMILY’s List about a potential campaign.

Other Democrats considering running include Maura Sullivan, a U.S. Marine veteran who’s reportedly a DCCC favorite, according to Crain’s Chicago Business. Carole Cheney, a district chief of staff to Rep. Bill Foster George (Bill) William Foster81 Nobel laureates endorse Biden's White House bid Trump payroll tax deferral finds few takers among businesses Former Obama Ebola czar Ron Klain says White House's bad decisions have put US behind many other nations on COVID-19; Fears of virus reemergence intensify MORE (D-Ill.), is “likely” running.

California’s 25th District Rep. Steve Knight

Knight has also been on Democrats’ target list since he was elected to Congress in 2014.

In 2015, Knight caught flak for his confrontation with a protester at an immigration rally, and his campaign initially had lackluster fundraising ahead of his competitive race. But he was reelected to a second term and outperformed Trump, with Clinton winning the district by nearly 7 points.

Katie Hill, executive director of a group that provides homeless services and housing, declared a run for the northern Los Angeles County seat.

At a recent town hall, Hill asked how Knight would have voted on the GOP’s ObamaCare replacement bill if it had reached the House floor. Knight said he wouldn’t discuss a “hypothetical,” earning loud boos from the crowd.

Jess Phoenix, a volcanologist, is “90-plus percent sure” she’ll run, according to the Los Angeles Times. She’s receiving help from 314 Action, a group that recruits people with science backgrounds to run for office.

Lawyer Bryan Caforio, who lost to Knight in 2016, is considering another run.