WASHINGTON — The retirement of Tom Harkin, a Democrat who has represented Iowa in the Senate for nearly 30 years, should be the kind of rare opportunity that sends the best and brightest of his state’s political class scrambling to get on the ballot.

But so far the only viable candidate to raise his hand is Representative Bruce Braley, also a Democrat. On the Republican side, one potential candidate after the other has taken a pass — the popular governor, his lieutenant governor, two congressmen and an ambitious state senator who said that he is not willing to have his life turned upside down.

The dearth of candidates for an open Senate seat reflects what former and current senators and those who once aspired to the office say is a sad truth: rarely has the thought of serving in the Senate seemed so unappealing.

Once considered an apex of national politics second only to the presidency, the “greatest deliberative body in the world” is so riven by partisanship and gummed up by its own arcane rules that potential candidates from Georgia to Kentucky, Iowa to Montana are loudly saying, “Thanks, but no thanks.”