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 CaseyRobert (Bob) Patrick CaseyNow is the time to modernize the OTC monograph system Dems walk tightrope on Pompeo nomination Overnight Energy: Trump NASA pick advances after drama | White House office to investigate Pruitt's soundproof booth | 170 lawmakers call for Pruitt to resign 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.