The Founding Fathers didn’t expect that serving in Congress would be a lifetime career. And for a century, it mostly wasn’t.

The first election in which more than half the incumbent members of the House of Representatives were re-elected was in 1898. Since then, the majority of House members have been returned in every election except the one in 1932.

That’s the context in which to weigh the fact that three incumbent Republican representatives who have been comfortably re-elected have announced they are retiring — and the rumors that more will do so.

Incumbents tend to know — and be known in — their districts. They usually win, whereas open-seat contests often result in changes of party control.

The three retiring Republicans are seven-termer Dave Reichert of Washington, seven-termer Charlie Dent of Pennsylvania and two-termer Dave Trott of Michigan.

Reichert was re-elected by a 60-40 percent margin last year in a district dominated by affluent suburbs to the east of Seattle. It also includes some Republican farm country east of the Cascades.

Donald Trump lost the district by a 48-45 percent margin, a little worse than Mitt Romney’s 50-48 percent loss in 2012.

Dent was re-elected by a 58-38 percent margin in a district that includes the industrial and suburban Lehigh Valley around Allentown. Trump carried the district 52-44 percent, more than Romney’s 51-48 percent margin.

Trott was re-elected by a 53-40 percent margin in a suburban district to the west of Detroit. Trump carried that district 50-45 percent, and Romney won it 52-47 percent.

So all three ran ahead of Trump in closely divided districts

Demographically, Pennsylvania’s 15th Congressional District is tilted to non-college-educated whites, among whom Trump ran stronger than traditional Republicans; Washington’s 8th District and Michigan’s 11th District are tilted to white college graduates, among whom Trump ran behind Romney and George W. Bush.

Democrats have been running ahead of Republicans on the generic voting question — which party’s candidate will you support for the House of Representatives? — by a 46-37 percent margin in the RealClearPolitics average.

That sounds big, but in the past, the generic vote has tended to overstate Democrats’ support, and an unusual percentage chime in as undecided. Also, the clustering of Democratic voters in relatively few urban and university districts means the party could win the House popular vote but still fall well short of a majority, as it did in 2012.

But as RealClearPolitics analyst David Byler has noted, the Republican generic numbers have been tracking close to Trump’s approval rating. That has risen just a bit during hurricane season but is still underwater in post-Labor Day surveys — at 39.5 percent approval, 56 percent disapproval.

His favorable/unfavorable numbers are negative, too, but they were similarly negative Nov. 8.

The nightmare scenario for House Republicans is that their candidates, especially in open seats, run no better than Trump in high-education districts and no better than traditional Republicans in low-education districts. That’s roughly what happened in the four seriously contested special elections this spring.

That puts at risk the 241-194 majority Republicans won in 2016.

The nightmare scenario facing Republicans like Reichert, Dent and Trott is that they get opposed by Trumpish (or Steve Bannonish) or tea party-type Republicans in their primaries and by well-financed Democrats, who have been lining up to seriously contest the general election.

Plus, the reward for winning is coming back to a House Republican Conference split between leadership loyalists and the House Freedom Caucus and dissed and possibly spurned by Trump.

Trump and the House Freedom Caucus types share a corrosive distrust of House Speaker Paul Ryan, but their views on important issues are often wildly divergent.

House Republican rebels insist on purism and are oblivious to the history that legislative majorities, if they stick together, can move policy significantly in their direction.

House Democrats — for example, Henry Waxman with the expansion of Medicaid — did this even in the Reagan years, but not by preventing the party’s House leadership from amassing majorities for the basic task of governing.

Republican incumbents may be choosing to retire to avoid harsh competition in primaries and in November. But they may also be motivated by something verging on despair over the fact that their party seems likely to fall far short of what it might reasonably have been expected to accomplish with the presidency and majorities in both houses of Congress.

In those circumstances, they seem to be behaving as the Founding Fathers expected and as politicians routinely did until 1898 — pursuing other endeavors and letting someone else endure the frustrations of trying to govern.

Michael Barone is a senior political analyst for The Washington Examiner, a resident fellow at the American Enterprise Institute, a Fox News Channel contributor and a co-author of The Almanac of American Politics. Click here to contact him, follow him on Twitter: @MichaelBarone, or click here to read previous columns. The opinions expressed are his own.