Why Democrats are feeling better about their Senate odds

Democrats are growing increasingly optimistic about their chances of holding the Senate this year amid a spate of favorable public polling and signs that some of the GOP’s top candidates are struggling to get their campaigns off the ground.

To be sure, Democrats have zero margin for error. The Senate is split 50-50 and any misstep or error — forced or unforced — could hand Republicans the majority in November. 

But for now, at least, strategists and operatives on both sides of the aisle say Democrats may have a real...