If more congressmen like Rep. Charlie Dent, R-Pa., start heading for the exits, it will become harder for Republicans to defend their House majority next year in what figures to be a challenging election cycle.

Dent is a leading centrist Republican representing a swing district President Trump won by less than 10 points. On Thursday, he announced he wasn't seeking reelection in a statement containing not too thinly veiled swipes at his own party's contributions to "ideological rigidity" and "dysfunction" in Washington, creating another open seat for Republicans to defend in the 2018 midterms.

"I'm afraid that this trickle is going to turn into a flood of moderate Republicans retiring because they don't want to have to defend Trump and deal with their far right colleagues anymore," said a GOP strategist who requested anonymity to speak candidly. "It's got to be exhausting and civilian life looks pretty good."

Dent, whose district went for Trump by 51.8 percent to 44.2 percent for Hillary Clinton in November, is already the third Republican fitting this profile to retire this year. Just the day before, Rep. Dave Reichert, R-Wash., said he wouldn't be running again next year. Clinton carried Reichert's district by 3 points in 2016.

Prior to that, Rep. Ileana Ros-Lehtinen, R-Fla., said she wouldn't run for reelection in 2018. Her district went for Clinton by nearly 20 points, although Trump won Florida statewide.

Republicans have a 24-seat majority in the House. This includes 23 Republican-held districts Clinton won in the presidential election and 40 where Trump received less than 50 percent of the vote. The GOP is undefeated in competitive special congressional elections in 2017, including one in a historically conservative-leaning Georgia district that Trump took by just 1.5 points.

In his statement explaining his decision to forgo reelection, Dent repeated his frequent assertion that he was a member of the "governing wing" of the Republican Party. "Regrettably, that has not been easy given the disruptive outside influences that profit from increased polarization and ideological rigidity that leads to dysfunction, disorder and chaos," he added, taking a swipe at conservative groups.

Dent's predecessor in the House, current Republican Sen. Pat Toomey, served as head of one such group, the Club for Growth. Toomey won his Senate seat after twice challenging centrist Republican Sen. Arlen Specter, losing the GOP primary in 2004 but amassing such a huge lead among primary voters six years later that Specter left the party in a failed effort to keep the seat.

Rep. Steve Stivers, R-Ohio, chairman of the National Republican Congressional Committee, praised Dent for his "leadership" and having "championed conservative values since taking office in 2005" while expressing confidence the party would retain his seat.

"Voters sent a clear message by delivering the district for President Trump last November — and we are confident that PA-15 will remain solidly under Republican control," Stivers said in a statement issued by the NRCC.

Tensions between centrist and conservative Republicans boiled over this year, especially during the healthcare fight. Members of the Freedom Caucus and the Tuesday Group each tried to pull their party's plan to repeal and replace Obamacare in opposite ideological directions, with Dent joining many centrists in voting against the final product that passed the House before stalling in the Senate, where similar divisions and a narrower majority prevented healthcare legislation from passing at all.

"I am disappointed that the House passed this bill which I believe will increase health insurance costs — particularly for low-to-moderate income Americans, increase the number of uninsured by up to as many as 24 million people, and undermine important protections for those living with pre-existing conditions," Dent said in a statement in May. "It is my hope that cooler heads will prevail in the Senate and that they will produce a better bill that is focused on improving healthcare for all Americans rather than the haphazardly constructed and hastily considered House bill."

Fellow centrist Rep. Tom McArthur, R-N.J., resigned as a chairman of the Tuesday Group after playing a role in negotiating with conservatives and getting the healthcare bill through the House. Dent remained a co-chairman of the group.

"I am grateful to my colleagues across the political spectrum and have been encouraged by their support," McArthur said in a statement. "That being said, it's clear that some in the Tuesday Group have different objectives and a different sense of governing than I do."

In addition to policy disagreements, many centrists complained they were being asked to take bigger political risks than their more conservative colleagues who generally represented safer, more Republican districts. One Republican operative lamented members from marginal districts being asked to "walk the plank" on bills conservatives with safe seats were voting against.

Trump's job approval rating sits at around 40 percent nationally, but it is lower in many swing districts. A SurveyMonkey breakdown of state-by-state Trump approval ratings released Friday showed the president remained popular in states like Wyoming and West Virginia, but was at 35 percent or less in 13 states mostly in the Northeast and Pacific West where the surviving Republican lawmakers tend to be more moderate.

For these reasons, Republican sources say they don't expect Dent to be the last centrist or swing-district GOP lawmaker to retire over the next two years. "We're lucky, frankly, more haven't already," said a Republican strategist advising centrist candidates, speaking on condition of anonymity.