Roughly 1/3 of Senate seats are up for re-election in November. Democrats are optimistic about their chances of winning control of the House, but their math in the Senate is tougher. Republicans hold 53 seats, and Democrats hold 47 seats, so they must pick up four seats to win a majority. They will have to win more conservative states to win a majority.

The seats held by GOP Senator Susan Collins in Maine, a state Trump has lost in each of his three runs, and retiring Senator Thom Tillis in North Carolina, which Trump won by only about 3 points last November, are viewed as Democrats’ best pickup opportunities.

Stephen Farnsworth, political science professor at the University of Mary Washington, told Newsweek the Senate “seems more likely to remain in Republican hands than not.”

“Democrats have good pickup opportunities in NC and ME—and perhaps an outside chance in Ohio. Even so, a very good election night for Democrats in the upper chamber would only bring the Senate to 50-50, with a Republican VP serving as the tie-breaker,” he said.