After months of anticipation, the 2026 race for Nevada governor came into focus on Monday, with the favorite for the Democratic nomination making his campaign official as he seeks to take down the Republican incumbent.

The race, one of the most prominent in the country next year in a critical battleground state, is heating up. In addition to the parties’ headliners, an unlikely challenger is already mounting a surprising bid. And a former governor may yet attempt a comeback.

The flurry of activity is all part of a growing effort among Democrats to take down one of the most vulnerable Republican incumbents: Gov. Joe Lombardo, who is running for re-election in a swing state that has not hesitated to oust its sitting officeholders in recent years.

Mr. Lombardo, the former sheriff of Clark County, home to Las Vegas, will nevertheless be tough to defeat. He has cultivated a reputation as a relatively moderate Republican focused on policy while avoiding much of the flamethrowing partisanship that has characterized G.O.P. politics in the Trump era.

Democrats’ best shot is likely to be Aaron Ford, the state attorney general who announced his entrance into the Democratic primary on Monday after signaling his intention to run for months. Mr. Ford is widely viewed as the favorite to win the nomination, though he will have company in the primary next June.

Mr. Ford, 53, would be Nevada’s first Black governor as Democrats strain to regain the trust of minority voters who voted for President Trump last year. Among working-class voters, Mr. Ford’s blue-collar background could be an asset.