A lot of the profiles for Ted Kennedy note how he became a major force in the US Senate, and US politics in general, despite his reputation as a lightweight when he took over his brother’s seat in 1962 at the age of 30. But Matthew Yglesias argues that this transformation was far from ironic and was even somewhat predictable:

…the fact that he had such an impressive career in part precisely because he initially got a job he wasn’t qualified for. The Senate operates largely on the basis of seniority. A guy who can enter his fifth term and only be 54 years old is a guy who’s going to be able to wield some major influence for a long time. And yet Massachusetts must have had many better-qualified potential senators who, had they gotten the gig, never would have acquired Kennedy’s legacy not just because they would have lacked Kennedy’s skills but because they would have been too young.

Assuming the seniority system remains in place, it might make sense to treat a US Senate vacancy the same as a US Supreme Court vacancy and select someone who can stay put for a couple of decades. (True, senators don’t have the lifetime job security that a Supreme Court justice does, but particularly in a state that leans so heavily toward one party as Massachusetts does, a reasonably competent incumbent can expect to be in Washington for a long time.)

That argument would make 49-year-old Jim McGovern the most sensible candidate from the state’s House delegation in terms of amassing clout. He’s younger than 57-year-old Mike Capuano, 54-year-old Stephen Lynch, and the seven other US reps. He’s also greener than 56-year-old Attorney General Martha Coakley and 52-year-old former US Rep. Marty Meehan.

Of course, youth will be a big advantage in the special election to replace Kennedy only if the typical voter cares about how much clout Massachusetts has in Washington 30 years from now. And US voters aren’t exactly known for long-term thinking.