A senator in the White House.(Perspective)

It's no secret that voters could make history in November by electing the nation's first female or black president. But it's also likely they'll do something the country hasn't seen in nearly five decades - choose a sitting senator for the job.

All three of the major parties' leading candidates are senators - Hillary Rodham Clinton and Barack Obama on the Democratic side, and John McCain on the Republican.

Since the founding of the country

Only two sitting senators have been elected president - Warren Harding in 1920 and John F. Kennedy in 1960.

Harding is ranked 40th out of 42 past presidents in the Siena Research Institute rating system, …