Kamala Harris' nascent presidential campaign has the wind at its back right now. But her entry into the race doesn't change her party's daunting Senate map, in which Democrats are playing defense in states like Montana, Ohio, Michigan, and Wisconsin.

On this episode of our podcast, On The Merits, Bloomberg Government senior reporter Greg Giroux says it will be tough for Democrats to hold onto the Senate unless Harris scores a surprisingly large victory and some downballot candidates ride her coattails to victory.

He also says Republicans have largely avoided the mistakes of two years ago, when several flawed candidates won primary races and went on to lose races that the GOP was initially projected to win.

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