Vice President Kamala Harris is building a lead over President Donald Trump in three must-win states for her campaign.Andrew Harnik/Getty Images; Stephen Maturen/Getty ImagesThe Harris campaign is showing new strength in must-win states ahead of the party's convention.In Michigan, Pennsylvania, and Wisconsin, Harris leads Trump 50% to 46% among likely voters.It's a reflection of the continued reset of the 2024 race after Biden's exit.Vice President Kamala Harris' presidential campaign is less than a month old but the latest New York Times/Siena College polls already show her leading former President Donald Trump in the critical battlegrounds of Michigan, Pennsylvania, and Wisconsin.Before President Joe Biden left the presidential race in July, he held a small advantage over Trump in an earlier Times/Siena survey of Wisconsin, but trailed the former president in Michigan and Pennsylvania.