With a relentless barrage of phone calls, mailers and targeted ads, local and statewide campaigns are now aggressively pursuing absentee voters — the most valued of voters, and the most vulnerable.

Absentee voters, who submit their ballots by mail, make up an ever-increasing share of the Florida electorate — the result of relaxed voting laws and aggressive campaign strategies. In the coming election, as many as one in four Florida voters will cast their ballots from home instead of a voting booth.

In Miami-Dade County, the share of absentee voters this fall could be even higher: Already more than 208,000 absentee ballots have been mailed to Miami-Dade voters since Oct. 5.

In the primary election in August, almost 40 percent of the votes cast in Miami-Dade were absentee. In some precincts in Hialeah and Sweetwater, as many as two-thirds of the votes were cast by mail, records show.

“If you do not work absentee ballots you will not have a successful campaign,” said political consultant Sasha Tirador, who represented several local candidates in the Aug. 14 primary.

That primary also showed the dangers of absentee voting: Miami-Dade police arrested two boleteros, or ballot-brokers, on charges of altering ballots of elderly or disabled voters. The ballot-brokers are also accused of collecting almost 200 ballots from Hialeah voters, violating a local ordinance limiting possession of multiple ballots.

Absentee-ballot fraud is nothing new, particularly in Miami-Dade, where two local elections were overturned in the 1990s because of phony and forged absentee ballots. In 1976, local elections officials tossed out piles of suspicious absentee ballots cast at Miami nursing homes.

“Absentee ballots seem to be prone to manipulation,” said Joe Centorino, director of Miami-Dade’s Ethics Commission and a former assistant state attorney who prosecuted several vote-fraud cases stemming from Miami’s tainted 1997 mayoral election. “Once those ballots go out, there’s no more control.”

But despite the recurring fraud problems, state lawmakers have repeatedly loosened the state’s absentee voting rules, making it easier to vote from home — while also making vote fraud harder to detect, critics say.

At the same time, the state has increased scrutiny of in-person voters by requiring those voters to provide photo ID at the polling place — a burden that absentee voters don’t have to bear.

“It is clearly easier to vote, with less obstacles, absentee than in person at the polls. And there’s more room for shenanigans,” said Murray Greenberg, the former Miami-Dade County Attorney who now teaches election law at the Florida International University College of Law.

In recent years, the Republican Party of Florida has aggressively promoted high absentee turnout among GOP voters. Republicans have dominated the Legislature as it has loosened absentee voting rules and cut the number of days for early voting, which tends to favor Democrats.

For candidates, absentee ballots present an alluring opportunity: Their campaigns can target these voters with mailers, ads, phone calls and at-home visits while the voters have the ballots in their hands.

Florida law now allows campaigns to track absentee ballots in real time, confirming on a daily basis who has voted and who still has a ballot at home. Campaigns pester the slackers with phone calls “until you drive them crazy,” said Dario Moreno, a campaign consultant and political science professor at Florida International University.