Early voting in the US presidential race begins on Thursday, and millions of people in key states will cast ballots in the weeks to come that could prove decisive on Election Day in November.
They did in 2008, when President Barack Obama's margin of victory relied to a great degree on early votes cast in such crucial states as Florida, Colorado, North Carolina and Iowa.
These days, a call to vote early is a standard plea in Obama's campaign speeches.
"Because in Iowa, you don't have to wait till Nov. 6 to vote. You can be among the very first to vote in this election, starting September 27," Obama told supporters Saturday.
Republican challenger Mitt Romney is looking to build up that early vote as well. But early voting has favored Democrats, drawing heavily from the African-American community.
Black churches in 2008 promoted "take your souls to the polls" programs, helping deliver churchgoers from Sunday services to polling places.
If votes cast on Election Day decided the 2008 election, Republican John McCain would have won in Florida, Colorado, North Carolina and Iowa.
But Obama won those states with an overwhelming early vote advantage, gained by mobilizing not only committed voters but also non-habitual voters with Internet ads, email and text messages and home visits and phone calls.
This time, putting votes in the bank early is even more crucial for Obama.
Amid a fragile economic recovery and a persistently weak job market, every voter who decides early is a voter who can't change his or her mind later if unemployment worsens.
The Romney camp is counting on four years taking their toll on Obama's supporters, lowering their intensity and making them a harder sell.
This means that today's presidential campaign looks much different from those of old, when massive get-out-the-vote operations were confined mostly to the final weekend and Monday before the election.
Now, voter turnout is becoming a two-month slog. That is why the airwaves are already clogged with television ads, mailboxes are cluttered with political mailings and people are picking sides even before the first presidential debates take place in early October.
"The old adage in Republican politics was a 72-hour campaign," said Scott Jennings, Romney's top aide in Ohio. "But really, that's a misnomer these days. We are going to be treating every day like Election Day, especially when the early voting starts."
Early voting has been expanding every four years, setting records in 2008, when more than three out of 10 votes were cast before Election Day.
More than half of the ballots in Colorado, Nevada, North Carolina and Florida were cast before Election Day, with Colorado leading the pack with 78% of total votes cast early.
This year, Idaho and South Dakota can begin early voting on September 21, followed later in the month by Vermont, Iowa and Wyoming.
Battleground states such as Ohio begin early voting October 2 and Florida on October 27.
Most states also allow voting by absentee ballot, provided voters offer an excuse, and those ballots become available beginning this month.
In all, 32 states and the District of Columbia allow voters to cast early ballots, by mail or in person, without having to give a reason.
Across the country, Republicans have worked to curtail early voting over the past four years.
Florida and Ohio officials are embroiled in lawsuits over early voting.
Republicans in Florida approved a law last year shaving the number of early voting days from as many as 14 to eight.
Early-voting advocates are challenging that, and a panel of three federal judges recently determined the changes could hurt participation by blacks.
In Ohio, another election battleground, the Obama campaign sued over a Republican-backed state law cutting off early voting for most people on the weekend and Monday before Election Day.
A federal judge on Friday agreed to restore the voting days, although Ohio's Republican attorney general, Mike DeWine, plans to appeal the ruling. Early voting in both states begins Oct. 2.
But whether this election can match or exceed the 2008 early vote is an open question.
"We're not dealing with a candidate who's running for the first time; we're not dealing with the establishment of an historic change, and we have an economic downturn," observed Kareem Crayton, a political scientist at the University of North Carolina who specializes in voting rights.
Paul Gronke, director of the Early Voting Information Center at Reed College in Oregon, said that without the level of enthusiasm and excitement that existed in 2008 the early voting patterns might build up more slowly.
He also noted that Romney has embraced some of the same social media techniques that Obama used in 2008 to motivate his early voters.
"For that alone, Obama has a bigger challenge," he said.