First time since 1960

That's because all three remaining candidates for president are current members of the United States Senate.  Whoever remains standing at the end of the process in November will defy history by becoming the first sitting senator elected to the presidency since JFK.

Much has been written this election season about the historic firsts with Obama, Clinton and McCain. Obama would be the first African-American president, Clinton would be the first woman president, and McCain would be the oldest person elected president in our history.

But there's another historic break from the past that is now all but guaranteed. For almost 50 years, every person elected to the presidency has been a governor or a vice president. This year -- barring any dramatic unforeseen circumstances -- that won't happen.

When Kennedy was assassinated in 1963, his vice president Lyndon Johnson became president after being sworn in on an emergency Air Force One flight from Dallas to Washington. Johnson had been the Senate majority leader before he became vice president, but he was not a sitting senator when he took the oath of the presidency.

Nor was Richard Nixon.  He too was a former senator, but his most recent job before becoming president in 1969, was as vice president to Dwight Eisenhower, leaving office in 1961.

Nixon was succeeded by his own vice president, Gerald Ford, after the Watergate scandal forced the president's resignation. But Ford couldn't win his own term and was defeated by a 1-term Georgia governor named Jimmy Carter.

Since that time, governors have dominated the White House.  Something about the sense of "executive experience" seems to appeal to Americans seeking a president, according to some political analysts.

Ronald Reagan, a former governor of California, was elected president in 1980. Bill Clinton, a governor of Arkansas, was elected in 1992 and again in 1996. And George W. Bush won in a controversial and contested election in 2000 and again in 2004.

The only two exceptions to the bias in favor of governors were in 1988 and, arguably in 2000. In 1988, the first George Bush, then a vice president to Ronald Reagan, defeated Massachusetts Gov. Michael Dukakis, and in 2000, Bill Clinton's vice president defeated Texas Gov. George Bush in the popular vote, although he lost the electoral college after falling short by 537 votes in the hotly contested state of Florida.

In fact, until John Kerry's nomination in 2004, the Democrats hadn't picked a senator to be their standard bearer since George McGovern's ill-fated 1972 campaign, which gave the Republicans a landslide victory.

The GOP hasn't done much better with senators.  The last senator to win the Republican nomination was Bob Dole, who went down to defeat against Clinton in 1996.