Like Brown, Nelson seemed for a time to be in some amount of jeopardy. Some polls in late July and early August saw Mack, who won the Republican primary Aug. 14, pulling ahead of the incumbent Democrat. But that bump proved fleeting, and Nelson remains the favorite to retain his seat.

There was one sign of encouragement for Republicans in the Times poll, however. Sen. Bob CaseyBob CaseyLive coverage: Senators grill Trump's Treasury pick Live coverage: Tom Price's confirmation hearing Senate Democrats brace for Trump era MORE (D-Pa.) held only a six-point lead over Republican challenger Tom Smith — a promising showing against an incumbent considered safe. While a Franklin & Marshall poll also released Wednesday gave Casey a 10-point lead, the Pennsylvania lawmaker's advantage has seen a significant dip from earlier this year. At the beginning of August, the Times gave Casey an 18-point lead, meaning Smith has gained 12 points in the past two months.