Thursday’s House vote on the GOP's ObamaCare replacement plan comes with significant electoral implications for vulnerable Republicans on the ballot in the 2018 midterms.

Republicans and the White House have massaged the bill for months in the hopes of striking a balance that satisfies both conservative and moderate Republicans. Lawmakers have been under intense pressure back home to oppose the bill, with protesters flooding town halls.

The House leadership can afford to lose 21 GOP votes while still passing the bill, with many of those defections expected to come from the most vulnerable Republicans.

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Ahead of the early afternoon vote, here are the 15 GOP lawmakers with the most at stake electorally, along with the lawmaker’s current stance in The Hill's Whip List and their district’s Partisan Voter Index rating — a metric compiled by the Cook Political Report that uses recent presidential vote results to characterize how a district will perform when compared to the national average.

Carlos Curbelo (FL-26)

Whip list position: Undecided

Cook rating: D+6

The two-term congressman’s district has the most Democratic rating from Cook of any congressional Republican, making him a prime target for Democrats. Curbelo, who easily won in 2016 by 12 points, recently tweeted that he has concerns with the bill. But with a vote looming, Curbelo is considered a "yes" on the GOP plan.

David Valadao (CA-21)

Whip list position: Undecided

Cook rating: D+5

Democratic presidential nominee Clinton cruised to victory by 15.5 points in Valadao’s district, which sits in the heart of California's San Joaquin valley. But Valadao has had just as easy a time, winning all three of his elections by double-digits in a district that was once safely Democratic.

John Katko (NY-24)

Whip list position: No

Cook PVI: D+3

Katko has been on House Democrats’ target list since he entered Congress in 2015. While he easily won reelection by 22 points last year, Clinton also carried the Syracuse-area district by almost 4 points. Before House Republicans pulled the initial bill from a floor vote, Katko said he couldn’t support that legislation in its “current form” and remains a no on the revised bill.

Mike Coffman (CO-6)

Whip list position: No

Cook rating: D+2

Coffman has shaken off repeated Democratic challenges, but Democrats continue to target him in a district where Clinton won by 9 percentage points. Last week, he said he would have voted no if the bill had hit the floor then, and after some consideration this week, announced he would vote no.

Erik Paulsen (MN-03)

Whip list position: Yes

Cook PVI: D+1

Paulsen's district was considered one of House Democrats’ reach districts last cycle. Former President Obama had narrowly carried it twice. While they were unable to flip his suburban Minneapolis district, Clinton won it by more than 9 points. If Paulsen’s district becomes competitive in 2018, that could signal a wave for Democrats as they look to take back the House majority.

Barbara Comstock (VA-10)

Whip list position: No

Cook rating: D+1

Comstock has been one of the top targets for Democrats ever since her 2014 election, and her Northern Virginia district keeps getting bluer in the presidential vote. Democrats are already making healthcare a major issue in her race, needling her for announcing her opposition to the first iteration of the March GOP plan after it became clear the plan wouldn’t receive a vote. This time, she told The Hill that she remains a no even after the most recent changes.

Jeff Denham (CA-10)

Whip list position: No

Cook rating: Even

The former Air Force veteran’s district sits east of San Francisco, where Clinton prevailed by 3 points in 2016. Denham won by only 3.4 points in the last election, his closest race in years. He had won reelection by more than 12 points in 2014 and by 5.4 points with Republican Mitt Romney on the ticket in 2012. Denham did not take a position on the first GOP healthcare bill but will vote no on Thursday.

Steve Knight (CA-25)

Whip list position: Undecided

Cook rating: Even

Clinton won Knight’s district, located just north of Los Angeles, by 6.7 points in 2016. Knight has carried it twice, both times by more than 6 points, but has been met by vigorous protests at town hall events in recent weeks. Knight’s office has asked attendees to provide identification proving they live in his district to gain entrance to his public events.

Ed Royce (CA-39)

Whip list position: Undecided

Cook PVI rating: Even

Royce is one of seven California Republicans whom Democrats are targeting in 2018. Royce, chairman of the House Foreign Affairs Committee, has been in Congress for more than two decades, but Clinton won his Southern California district by nearly 9 points. A Royce spokesperson told The Hill that he has serious concerns with the revised bill.

Darrell Issa (CA-49)

Whip list position: Undecided

Cook rating: R+1

The former House Oversight Committee chairman made enemies with his investigations, meaning that Democrats are even more eager than usual to see him out of office. And Issa’s 5,000-vote margin of victory in a district Clinton won by 7.5 percentage points last year only emboldened them. Issa told local reporters he is “undecided and still reviewing the changes to the bill.”

David Young (IA-3)

Whip list position: Lean yes

Cook rating: R+1

Young co-sponsored the last-minute amendment offered by Rep. Fred Upton (R-Mich.) and appears to be moving closer toward a yes vote based on that deal. The Iowa Republican has been punished before for opposing the first iteration of the bill, with the Congressional Leadership Fund, a prominent super PAC tied to Congressional Republican leadership, pulling its support for his reelection effort.

Will Hurd (TX-23)

Whip list position: Undecided

Cook rating: R+1

Clinton carried Hurd’s West Texas district by more than 3 points in 2016. Hurd’s Hispanic-majority Congressional district stretches some 800 miles along the Texas-Mexico border, where Trump hopes to build a wall. Hurd has edged out former Rep. Pete Gallego Pete Pena Gallego4 Texas GOP congressional primary runoffs to watch GOP candidate scores upset win in Texas state Senate runoff Koch group launches digital ads in tight Texas House race MORE (D-Texas) there by less than two points in the last two elections.

Patrick Meehan (PA-7)

Whip list: No

Cook rating: R+1

Clinton carried Meehan’s district in the Philadelphia suburbs by 2.3 points, making him a top Democratic target in 2018. But Meehan cruised to victory in 2016 nonetheless, winning by nearly 20 points.

Leonard Lance (NJ-07)

Whip list position: No

Cook PVI: R+3

House Republicans looked to sway Lance, a member of the moderate Tuesday Group, to support the ObamaCare repeal bill. He opposed the first bill and has maintained that same position about the revised legislation. Lance has been in Congress since 2009 and has easily won reelection by more than 60 percentage points, but Clinton won by a little over 1 point in 2016 and two Democrats have already declared challenges to Lance.

Mimi Walters (CA-45)

Whip list position: Yes

Cook PVI: R+3

Since the initial repeal bill, House Democrats have stepped up their attacks on Walters for advancing the bill out of committee. Walters hasn’t been a past target, but the healthcare bill coupled with Clinton winning her district by more than 5 points has made her a top 2018 target. Walters has already drawn at least three Democratic challengers, including a former student of progressive Sen. Elizabeth Warren Elizabeth WarrenNo new taxes for the ultra rich — fix bad tax policy instead Democrats back away from quick reversal of Trump tax cuts It's time for newspapers to stop endorsing presidential candidates MORE (D-Mass.).