The phrase "to steal the election" means manipulating the voting process or using unfair tactics to gain an advantage and win an election, instead of winning fairly through the support of voters. Full definition
The history of election fraud, with its many techniques and variations, is pretty rich — people have been trying to steal elections since elections were invented. (politics.stackexchange.com)
Democrats will quit blaming James Comey, Vladimir Putin and the Grinch Who Stole the Election for Hillary Clinton's loss — and admit she was just a lousy candidate. (nypost.com)
Joseph G. here, we need you to take care of some Republicans I disagree with and who stole the election from Hillary. (nystateofpolitics.com)