FORT LAUDERDALE, Fla. – Florida Democrats are building a substantial lead in mail-in ballot requests for November’s presidential election even as their registration advantage shrinks, but questions remain about whether that will be a boon for Joe Biden as he tries to wrest the nation’s largest swing state from President Donald Trump.The Florida secretary of state’s office shows that 2.4 million Democrats have requested mail-in ballots compared with 1.6 million Republicans — a 767,000 request advantage as the coronavirus pandemic makes some voters leery of entering a polling place.