PORTLAND, Maine — She is not on the ballot this fall, yet the fight over Susan Collins’ political future is already raging.

Interest in the Maine Republican senator’s 2020 re-election has exploded in the days since she cast the deciding vote to confirm President Donald Trump’s Supreme Court pick — a vote that helped transform the balance of power on the nation’s high court for a generation and suddenly complicates Collins’ path to a fifth term.

Half a dozen Democratic prospects are openly considering running against the Republican political powerhouse, while an online fund has generated $3.6 million — and counting — for Collins’ ultimate Democratic challenger. The would-be candidates include Susan Rice, who had been one of President Barack Obama’s closest aides. Rice is not currently a Maine resident — she has family ties to the state — but would bring political celebrity that could make it difficult for the state’s shallow bench of lesser-known Democrats to stand out.

The emergence of a crowded field in a Senate contest two years away underscores the extraordinary political moment triggered by the debate over Supreme Court Justice Brett Kavanaugh.

Fighting allegations of sexual misconduct from three decades ago, he won confirmation by a razor-thin margin on Saturday over the screaming objections of Democrats and women’s groups in all corners of the nation.

Collins’ Alaska colleague, Sen. Lisa Murkowski, was the lone Republican to oppose the nomination. Now, Alaska GOP officials are considering whether to seek a replacement or encourage her not to seek re-election as a Republican when her term expires in 2022.