Many of the House members who are leaving are centrist Republicans, which could leave the GOP caucus more dominated than ever by the party’s conservative wing. Democrats, meanwhile, are losing some of the last of their party’s conservative “Blue Dog” wing.

Some of the retirees from the House—and most from the Senate—are committee chairmen or skilled legislators like former House Education Committee Chairman George Miller (D., Calif.), who announced his retirement this week.

Adding to those ranks, House Armed Services Chairman Howard “Buck” McKeon (R., Calif.) is also expected to announce Thursday that he won’t seek re-election, according to a GOP official familiar with his plans.

In recent years, many retirements have been propelled in part by a reaction to the polarization of Congress and the gridlock that has made it harder for lawmakers to make their mark. But the exodus of legislative veterans and pragmatists, in turn, could exacerbate the problem, leaving Capitol Hill increasingly populated by a younger generation of politicians inexperienced in the dying art of legislative compromise.