In 2000 Al Gore notoriously lost the election for President in Florida. The official Florida tally gave Bush the win by 537 votes (48.847 percent to 48.838 percent), while Nader racked up 97,488 votes.
...
In the 2016 New Hampshire Senate election, conservative independent candidate Aaron Day won about 18,000 votes. Given his political leanings, it is likely that the vast majority of his voters otherwise would have voted for incumbent Senator Kelly Ayotte, who lost to Governor Maggie Hassan by about 1,000 votes, thus costing Ayotte reelection.