While I agree with the gist of the article, it’s a bit misleading to say that neither of the other 2 Senators had 2nd terms. They both died in office. Based on all polling and information, both Harding and Kennedy easily would have won reelection had they survived and ran.
The pattern may yet continue.
True, certainly of Kennedy (I wasn't around when Harding died). But the salient point should be that, Harding excepted, Senators only beat other senators. Which means that it was stupid to nominate McCain or any other senator in ' 08. Any of the governors who contended for the nomination would have done better than McCain - and very likely would have won.
The other point to make is that cream rises to the top quickly; it's up or out in the presidential sweepstakes. Once you become a governor or senator, the clock starts ticking - and if you don't attain POTUS or at least VP within 14 years, you ain't likely ever to be elected POTUS.
So trying to elect a three-term senator as POTUS is doubly a fool's errand.Oh, and BTW a VP is not an executive, and only two sitting VP's have ever been elected POTUS (three counting Adams, who was elected VP before the 12th Amendment changed the election process for VP). Put differently, only Andrew Jackson and Ronald Reagan won third terms vicariously thru their sitting VPs who had been their running mates eight years earlier.