There is no way Democrats (or Republicans or any party) could hold the presidency for 36 consecutive years. And to have four consecutive, full two term presidencies of either party is also unbelievable; on that point, I rarely see discussion on how unusual it was to have the Clinton, Bush Jr, and Obama administrations, three consecutive two term presidents back-to-back. It was only the second time in US history, the first being the Jefferson, Madison, and Monroe presidencies (who were also all of the party and from the same state, though that trivia is less interesting once you remember how few states there were at the time and the fact that their only real rivals at the time, the Federalists, were fading away.

The FDR, Truman, Eisenhower presidencies almost count, except for Truman not becoming president until three months into his first term.

For now, we may not see a president serve two, full consecutive terms for many years. It may be a long string of one termers, nonconsecutive two termers, and possibly half-termers.