Hillary Clinton and Donald Trump are arming up for a possible post-Election Day battle.

Clinton is assembling a voter protection program that has drawn thousands of lawyers agreeing to lend their time and expertise in battleground states, though the campaign isn't saying exactly how many or where. It is readying election observers in Florida, North Carolina, Pennsylvania, Ohio, New Hampshire, Iowa, Nevada and Arizona to assess any concerns -- including the potential for voter intimidation -- and to verify normal procedures.

The Republican National Lawyers Association, which trains attorneys in battleground states and in local jurisdictions where races are expected to be close, aims to assemble 1,000 lawyers ready to monitor polls and possibly challenge election results across the country. Hedge fund manager Robert Mercer, one of Trump's biggest backers, has sunk $500,000 into the group, its biggest donation in at least four presidential elections, Internal Revenue Service filings show. 

"We are fighting for open, fair and honest elections," the association's executive director, Michael Thielen, said in an e-mail.

Most discussion about the potential for a contested election until now has revolved around the premise of a Trump loss, his contention that the election is "rigged" and his refusal to say ahead of time that he would concede. But since FBI Director James Comey's controversial disclosure on Friday that he is reviewing newly discovered e-mails possibly related to an investigation of Clinton, several polls have shown the race tightening considerably.

Although Clinton still holds an advantage -- currently 2.5 percentage points in the RealClear Politics average of national polls -- the developments have raised the prospect of a much closer than expected result and a previously unforeseen question: Would Clinton refuse to concede and wait for recounts and certified results or initiate legal action if she narrowly loses one or more battleground states decisive to the election.