With control of the Senate on the line, the drama surrounding President Joe Biden is an unwelcome development for Democrats. They are defending far more Senate seats than Republicans this year. They have seats on the line in the presidential swing states of Pennsylvania, Wisconsin, Michigan, Nevada and Arizona. Incumbents in the conservative states of Montana and Ohio are nervous, too, and were already keeping their distance from Biden. But the turmoil surrounding Biden is especially delicate for Pennsylvania Sen. Bob Casey. He's long been seen as one of the safest bets for Democratic incumbents running in swing states across the country this year.
