The Electoral College has been attacked almost from the start. Over 200 years, more than 700 proposals to eliminate or revise it have been introduced in Congress, and more constitutional amendments have been proposed to change the system than on any other subject, according to the National Archives. A Gallup poll last year found that 62 percent favored a constitutional amendment making the popular vote decisive.

“If you were to have a repeat of that except the popular vote winner was the Republican and the Electoral College winner was the Democrat this time, then you would have had each party burned by the Electoral College over the course of 12 years, and that might be conducive to a serious look at reform,” said Robert W. Bennett, a Northwestern University law professor who has written extensively on the Electoral College.

Less likely is a tie, 269 to 269. If that happened, strategists envision an intense postelection campaign of state-by-state recounts, lawsuits, qualification challenges, efforts to flip electors, horse trading and pressure on members of Congress. The result would be a highly volatile 11-week obstacle course to Inauguration Day that would leave the country uncertain for a time about its next president and potentially undermine the credibility of the winner.

“If this election does require some extra innings, we have plans in place to deal with that,” said Bill Burton, a former Obama aide and co-founder of a super PAC supporting the president. “But the odds of that are infinitesimally small.”