The primaries will select candidates for the general elections in November, when many governors, one-third of Senators and the whole of the House of Representatives will be elected across the United States. Seven other states as well as California were voting last night.
These contests will be minutely examined for what they tell about the balance of power two years from a presidential election. But the main theme is non-partisan - the power, and limits, of money.
Money has been pivotal to the primary race for Governor, with three Democrats competing for the nomination and one Republican.
Al Checchi, former co- chairman of Northwest Airlines, spent more than $30m (pounds 18m) promoting himself. Yet he looks set to trail Gray Davies, California's Lieutenant Governor, who spent a mere $12m.
Congresswoman Jane Harman, the wife of a wealthy stereo-equipment maker, unloaded $20m, and much good did it do her. The victor will face Republican Dan Lungren in the fight to replace Governor Pete Wilson, also a Republican.
Since the more monied candidates have not done well, the lesson which much of America's mainstream media has drawn is that money doesn't matter. That seems quixotic.
The California race has been consumed by dollars, with millions frittered away on the gubernatorial race and other contests for national and local office. As much as $100m has been spent, equivalent to the sums normally expended in a presidential election.
Darrell Issa, a car-alarm millionaire, spent about $8m in an effort to win the Republican nomination to contest one of the state's Senate seats. He was trailing state treasurer Matt Fong; but that also had something to do with embarrassing stories that came out about Mr Issa, such as his arrest for car theft (the charge was dismissed). Mr Fong looked likely to win, and could well unseat incumbent Democrat Barbara Boxer.
Cash has become so important partly because the primaries are open. That means voters of any affiliation can decide who will be the Democrat or Republican nominee, so candidates have sought to appeal to as wide a constituency as possible. Television has been the key weapon.
The primaries certainly open up the question of what money can and cannot do. With the economy booming and few serious problems on the horizon, voters seemed to prefer experience and known faces to rich outsiders.
Mr Davies, for instance, ran under the rubric of "Experience money can't buy". But the fact that money does not always win does not mean it isn't important - Checchi might well not have figured at all without his $30m.
Cash is also at the centre of one of California's ballot propositions, which seeks to require unions to get the permission of members before spending cash on politics. Proposition 226 has sparked the ire of the union movement, which has spent $15m to combat it. It looked uncertain last night whether the measure would pass.
Money will dominate the rest of the year, as candidates prepare for the November election. Although this is an off-year election, there is a chance that control of the House of Representatives could slip from the grasp of the Republicans. There are also a number of hard-fought Senate and gubernatorial races in prospect. Money and television will be at a premium, something that concerns many.
New donors keep emerging to fuel the campaign fires. The latest is Bill Gates, and Microsoft, who, after staying away from the political fray for years, has suddenly become a big-money donor to the Republicans. It may be coincidence that this comes as the (Democrat) administration takes on Microsoft in a high-profile anti-trust case.
Money has long been the weakest point of the American political system, opening it up to a variety of forms of legalised corruption. Congress is currently examining a flood of campaign finance measures, but none of them seems likely to succeed: not this year, of all years.Reuse content