Democrats keep doing surprisingly well in special elections. The party's most vulnerable Senate incumbents are running ahead of their rivals in key battleground states. One of Democrats' signature issues " reproductive rights " has repeatedly proved a winning message. And yet Joe Biden is struggling to pull even with Donald Trump. It's another ominous sign for the president: Even as other Democrats are running strong, the party's down-ballot successes aren't translating into momentum at the top of the ticket. Biden trails Trump in many of the states he needs to win to keep the White House. His job approval is underwater. And the coalition of voters that ushered him into office four years ago is fraying.