IOTL Nixon proposed a single six-year term like they currently have in the Philippines. WI that passed? How would that affect US politics? POD 1968. Perhaps the rule that if the Veep succeeds during the term, then they're eligible for re-election, like GMA was in 2004. Otherwise if they've served more than three years they're barred from re-election. Tell me what you think of this list with a January 1968 POD.
Richard Nixon (R-CA): Jan. 20, 1969- Jan. 31, 1975
Robert Kennedy (D-NY): Jan. 31, 1975- Jan. 31, 1981
Henry Jackson (D-WA): Jan. 31, 1981- June 10, 1986*
Lloyd Bentsen (D-TX): June 10, 1986- Jan. 31, 1993
Robert Dole (R-KS): Jan. 31, 1991- Jan. 31, 1999
Al Gore (D-TN): Jan. 31, 1997- Jan. 31, 2005
John McCain (R-AZ): Jan. 31, 2005- present
I find it hard to believe that a 6 year term would pass. People like voting for President every 4 years, I think. If it did, it probably wouldn't pass until after Nixon's first term, as it would require a Constitutional Amendment.
Assuming it did pass, I find the idea that Scoop Jackson could be elected President in 1980, or the idea that he would ever win the Democratic nomination at all, to be very implausible. Otherwise, that seems pretty reasonable.
I think it is possible, and if Nixon managed to get Congress to pass it during his first term (given his popularity, the Dems in Congress might see it as the easiest way to get him out of office rather then risking another four years), we'd eliminate Watergate. I would say that if Nixon was willing to not be grandfathered (ie it would apply to him, rather than he be able to run for a 6 year term after his four year term), then it would have a better chance.
If Nixon got it passed and applied to him, then the next presidential election would be in 1974. I think the winner there might be Reagan. The real question will be how Reagan handles the Iranian Revolution and the Embassy Crisis....
Then in 1980 we'd likely see a changeover to the Democrats. It might even possibly be Edward Kennedy, though his past may prove problematic. Still, it might be him. The economy is probably still having problems, and after 12 years of Republicans having an echo of Camelot may sound good to the electorate.
In 1986 things will have improved economically, but I could see the nation being a bit down on philandering by then (Teddy wasn't reformed by then), so if Hart makes it to be the candidate which is possible, he might be against George H.W. Bush and I can see the Bush campaign digging up Hart's own philandering (all of this is speculation, but reasonable speculation based on the trends and our own history). We might see an alternate Gulf War here, but it is unclear.
By 1992 the nation might be ready (again) for the Comeback Kid and Bill Clinton in the White House.
In 1998 after another philanderer in the White House the nation might be ready for someone a little more solid. I think it might be Bob Dole's year. While we are likely to still see the rise of Al Queda during this era, it is not clear whether they'd be as successful.
The result in 2004 depends on whether a 9/11 level terrorist event transpires during the middle of the Dole years. If so, I think the nation might be still security minded and we can see John McCain as the winner. If no 9/11 level event, then the nation might be ready for its first woman president, Hillary Clinton. This may be seen as one of the most cordial presidential elections in years. Without the stinging election against papa Bush in 1992, I'm not certain we see George W. Bush running for president.
What about 2010? Could be rising star Barak Obama's year no matter who won in 2004.
So far this came out oddly parallel, but the six year term is midway between 4 and 6 years, which makes it a similar political cycle many times.