You’ve heard of the “October surprise,” where candidates hold onto something negative about their opponent, then spring it at the last moment so the opponent won’t have time to respond much before Election Day?

Well, forget that model, which is about as modern and workable today as a Model T.

Mail-in ballots – known as absentee ballots when they were available only to voters who swore they’d be out of town on the day of voting – have vastly changed the dynamic of California elections.

Hold negative news about your rival until Nov. 4 this year – the day before Election Day – and a campaign manager might as well have just squandered his/her ammunition. For most votes are now cast well in advance of that deadline.

This was never more clear than in the June primary, when only about 31 percent of the state’s registered voters bothered to participate, and 65 percent of those folks did so by mail. This was a new record, surpassing the 62 percent of ballots cast by mail in a May 2009 special statewide election.

Anyone who doubts that the massive mail-in vote has changed things need only think back to almost exactly two years ago. That was when, in late September, celebrity feminist lawyer Gloria Allred came forward with the news that a client, illegal immigrant Nicky Diaz, had worked as a maid in the home of Republican gubernatorial candidate Meg Whitman for years until she was dismissed just days before Whitman announced her candidacy.

Allred also produced evidence that Whitman either knew or should have known her client was undocumented.

In other years, this might have been an October surprise, sprung on Whitman during the campaign’s last week when she’d have little chance to do anything about it.

But it came at least a month earlier. Why? Because 48 percent of the general election vote that year was cast by mail, and everyone in politics knew that would happen. It’s true, of course, that both Allred and Democrat Jerry Brown’s campaign adviser Steve Glazer denied that the campaign had anything to do with the timing of Allred’s press conferences.

Still, there’s no question that Allred revealed the Diaz story only about one week before county voting officials began sending out sample ballots, absentee voting applications and actual ballots for voters signed up to vote by mail in all elections. Those packages go out beginning 29 days prior to all statewide elections.

This year, that means they’ll be mailed on or about Oct. 7, with voters starting to send in ballots about one week later.

 The new timetable means candidates can no longer hold their money and ammunition until the last week or so before an election. Instead, they must advertise and spend heavily all through the last six weeks.

So even though the only statewide race this fall involves well-funded Democratic U.S. Sen. Dianne Feinstein against the almost unknown and underfunded Republican autism activist Elizabeth Emken, expect plenty of ads and slick mailers to begin airing and arriving on televisions and in mailboxes starting late this month, continuing right through Election Day. Well over $200 million will be spent on ads and mailers this fall for propositions and candidates for Congress and the Legislature, even if spending on the Senate race figures to be relatively light.

But don’t expect many last-minute surprises. The days are long gone when Democratic operative Bob Mulholland could reveal just five days before a 1992 election that GOP Senate candidate Bruce Herschensohn had frequented a Hollywood strip joint, or when Republican strategist Murray Chotiner could wait until the last moment to make “pinko Commie rat” imprecations against Richard Nixon’s rival in a 1950 Senate vote.

Neither Herschensohn nor Helen Gahagan Douglas had time to respond effectively to the innuendos against them, and that may have swung both those races.

Wait that long today, and it’s possible fewer than half the actual voters would be in position to respond. Which could make any such revelation too little, too late. To reach all, or almost all, voters today, both ads and surprise revelations must come much earlier, either by the end of September or in very early October.

All of which means the full implications of the late-1970s law opening mail-in voting to all who want it are only now becoming completely clear and effective. For sure, that law has forever changed election dynamics in California and the 23 other states with the same absentee voting freedom.