The election could be won or lost weeks before Election Day thanks to early voting that has now spread in one form or another to more than half the states.

With early voting kicking off Thursday in the critical swing state of Iowa, and with more swing states following close behind, including Ohio next Tuesday, Barack Obama and Mitt Romney will be banking real votes long before the frenetic final days of the campaign.

“I am forecasting in this election cycle that about 35 percent of the vote will be cast before Election Day,” George Mason University professor Michael McDonald, who researches early voting behavior, told TPM.

“We know 78 percent of all votes in Colorado were cast prior to Election Day in 2008, and it probably will be around 85 percent in 2012. The election will essentially be won or lost before Election Day unless it’s a tight, narrow, razor-thin margin.”

With more than one-third of the votes nationwide expected to be cast early, Romney’s already shrinking window to erase President Obama’s current lead in public opinion polls before Election Day is closing even faster. While the presidential debates, for instance, remain Romney’s last best hope to shake up the current dynamics of the race, many voters will have already cast their ballots before all the debates are held. Time is running out.

The prevalence of early voting in 2012 — either via in-person early voting or no-excuse absentee voting — continues the modern trend. Some 30.6 percent of the electorate voted early in 2008, but the percentages were much higher in battleground states like Florida (51.8 percent), Nevada (66.9 percent), and North Carolina (60.6 percent).

Ohio, where Obama is surging in public opinion polling, is poised for the biggest boost. Recently the Obama campaign successfully blocked the state in federal court from eliminating three early voting days. But the bigger news is that election officials, for the first time, are sending every single registered voter in the state an absentee ballot request form. According to RealClearPolitics, the Romney campaign is forecasting that the changes will spike the early voting rate from 25.2 percent in 2008 to 45 percent this year. Absentee voting begins on Oct. 2, the day before the first presidential debate.

“How many of you have already gotten your absentee ballot applications?” Sen. Rob Portman (R-OH) shouted at an Ohio rally on Tuesday before Romney took the stage. “The best thing we can do right now is bank votes, so vote absentee!”

One exception where the rules have moved in the opposite direction is Florida, which cut its number of early voting days from 14 to eight. The effects of the change are still unclear, however, especially as individual counties might offer longer voting hours.

Democrats dominated early voting in 2008 thanks to high enthusiasm among the base, an unprecedented ground game, and a huge cash advantage over John McCain. This time around, Republicans say things will be different: They have vastly improved resources thanks to stronger fundraising and more assistance from outside groups.

The Romney campaign says it has met many of McCain’s 2008 grassroots benchmarks weeks ahead of schedule. Among the stats cited, officials say they’ve knocked on one million more doors already than in the entire ‘08 campaign and made seven times as many phone calls as Team McCain volunteers had at the same point in the race. Conservatives groups and Republicans also ran successful early voting programs in victories across the country in the 2010 elections, though it should be noted that the midterm electorate is demographically much more conservative than the expected presidential electorate.

For its part, the battle-tested Obama campaign is counting on its own turnout operations to counter the expected advantage in late advertising dollars from Republicans and their allies.

“By encouraging our supporters to vote early, we can focus our resources more efficiently on Election Day to make sure those less likely to vote get out to the polls,” Obama campaign spokesman Adam Fetcher said in an e-mail. “While Mitt Romney and his allies are counting on big ad buys full of false attacks in the final weeks, we’ve made early investments in battleground states — where we’ve been registering folks and keeping an open conversation going with undecided voters for months — to build an historic grassroots organization that will pay off when the votes are counted.”

There are early indications in first-to-vote Iowa that the Obama campaign’s work may be paying off. While the GOP has made gains in voter registration since 2008, Democrats have made five times as many absentee ballot requests, a figure that is alarming some state Republicans.

Former Iowa Republican Party chair Craig Robinson, who now observes politics in the state closely as editor of The Iowa Republican blog, said Romney’s early vote efforts in the Hawkeye State so far fall far short of where John McCain’s were four years ago.

“There was quite a bit of mail being sent out,” Robinson recalled Tuesday. “The McCain campaign was fundamentally sound. I don’t have evidence of that yet from the Romney campaign.”

Robinson said he’s seen no early vote mailers from the Romney campaign so far. He fears Romney has missed the boat on early voting, leaving the Democrats to bank perhaps thousands of votes weeks before Election Day.

“I’m wondering what the Romney victory effort is doing in terms of early voting,” he said, “because I’ve seen some numbers that are big for Democrats and I’m wondering have they neglected it too much? Is it too late?”