California has done it again: rescheduled its presidential primary so that it will vote earlier in the presidential selection process. Instead of voting in early June, at the end (or just about the end: Utah voted later last time) of the primary and caucus system, California will now vote in March. Of course that may not be early enough to make California the central focus of presidential politics. In the 2008 cycle it voted in February, and even then 33 states voted earlier or on the same day.

Which is not to say that California has not made a difference in selecting presidential nominees. Voting in June, it provided narrow but decisive victories for Barry Goldwater over Nelson Rockefeller in the 1964 Republican primary and for George McGovern over Hubert Humphrey in the 1972 Democratic primary. From those results, and from Ronald Reagan's success in the 1966 Republican gubernatorial primary and the 1966 and 1970 general elections for governor, some (including me, at the time) drew the conclusion that California was partial to the (arguably) extreme candidates of both parties, and would tend to tilt their nominations in that direction.

There was a certain tension between that idea — that California was somehow at the leading edge of both conservative and liberal politics — and that it was a reasonable bellwether of national opinion. In support of the latter view, however, you could cite data that showed California voting very much like the nation as a whole in presidential general elections, generally not varying as much as 5 percent off the national Democratic and Republican percentages (more in 1968, when George Wallace took 14 percent of the national vote but won only 7 percent in California).

Thus California, the most populous state since 1963, followed in the tradition of New York, the most populous state from the 1810s until 1963, in voting in line with the national average.

California doesn't vote much like the rest of the nation any more. It favored Hillary Clinton over Donald Trump by a 30 point margin, the second most Democratic result (after Hawaii) in the nation. California voted 1 to 3 percent more Democratic than the nation in 1988, 1992 and 1996. Since then it has shifted to become more Democratic than the national result: 5 percent more in 2000, 6 percent more in 2004, 8 percent more in 2008, 9 percent more in 2012 and 13 percent more in 2016. This is the first time in American history that our largest state has voted at one end of the partisan spectrum.

These results make mincemeat of the argument that California ought to go first because it's typical of the nation as a whole. And of course California's large size means it can't be the kind of venue where personal campaigning and grassroots organization can propel an otherwise little known candidate ahead, as Iowa and New Hampshire have repeatedly done.

Quite the contrary: California requires huge amounts of money and favors candidates with national (or California) name identification. Perhaps that would help Kamala Harris, elected California's attorney general in 2010 and 2014 and U.S. senator in 2016. But it's not clear that helping Harris helps the Democratic party. She seems well to the left of Hillary Clinton on many issues, and while that's not a general election problem in California, it could be in most of the rest of the country.

Clintons have won the last three seriously contested California Democratic presidential primaries, in 2016, 2008 and 1992, though not by overwhelming margins; none of these victories has been decisive in clinching the nomination. Curiously, California has been more crucial in determining Republican nominations.

In 2008, when California voted in February, John McCain beat Mitt Romney there by a 42 percent-34 percent margin in popular vote; but since Republicans award delegates winner-take-all by congressional districts, and McCain carried 48 of the 53 districts, the result prompted Romney to leave the race.

In 2000, when California voted in March, George W. Bush only beat McCain by nine points (52 to 43 percent), but his carrying 44 of the 52 congressional districts gave him a big delegate lead. It's unlikely that California's Democratic legislators and governor are giving much consideration to an early primary's effect on the Republican nomination; perhaps they suppose Donald Trump could be vulnerable in the state in 2020. But California Republicans voted 75 percent for Trump in 2016, albeit in June, when all other candidates had withdrawn.

So despite California Democrats' hopes that an early presidential primary date will give the state greater influence in selecting a Democratic nominee, past history suggests that that's not likely — and that there's a risk that California, newly installed at the left extreme of the political spectrum, will tilt the process toward an unelectable left-wing nominee.

And it seems likely — at least this is how it's worked out in the recent past — that an early California primary will be determinative in the Republican nomination race, which may or may not be in Democrats' interests. Politicians fiddling with the presidential primary schedule should always remember that there's no way to repeal the law of unintended consequences.