Republican presidents brain teaser

I discovered an interesting fact a few days ago; it's a small and most likely useless item of history (as well as not really a "brain teaser" as such), but one I feel worth sharing. To begin with, I'll list all Republican Presidents of the United States since 1948 who won election to the position:

Dwight D. Eisenhower

Richard Nixon

Ronald Reagan

George H. W. Bush

George W. Bush

So other than being president, what is distinct about these five men? Have a think for a moment, but if you'd like a clue, carefully look at these names:

Dwight D. Eisenhower/Richard Nixon - 1953-1961

Richard Nixon/Spiro Agnew, later Gerald R. Ford - 1969-1974

Ronald Reagan/George H. W. Bush - 1981-1989

George H. W. Bush/Dan Quayle - 1989-1993

George W. Bush/Dick Cheney - 2001-2009

I excluded Ford (1974-1977) from the first list because he was never elected to president. Do you see any pattern now? I'll give you one more hint:

Herbert Hoover/Charles Curtis - 1929-1933

I shall reveal the answer in tomorrow's post. Until then, feel free to guess away!