WASHINGTON — Thousands of attorneys, representing the two major presidential candidates, their parties, unions, civil rights groups and voter-fraud watchdogs, are in place across the country, poised to challenge election results that may be called into question by machine failures, voter suppression or other allegations of illegal activity.

Election litigation has become an institutionalized part of campaigns since the 2000 presidential race, when Vice President Al Gore won the popular vote but Texas Governor George W. Bush captured Florida’s 29 electoral votes — and the White House — after 36 days of lawsuits, recounts and court actions. The volume of court fights triggered by contests up and down the ballot has doubled in the past 12 years, said Richard Hasen, a professor at the University of California at Irvine.