The Upshot’s new Senate election forecast gives Democrats a 60 percent chance of winning control of the chamber in November.

Included within this 60 percent is a 17 percent chance that the Senate ends up evenly split with a Democratic vice president providing the tiebreaking vote.

By our count, the Democrats need to win five seats among the 11 most competitive races. (The Democrats will need to win six if Donald J. Trump wins the presidential race; we put Mr. Trump’s chances of winning at only 11 percent). Ten of these seats are held by Republicans, and one by a Democrat, Harry Reid of Nevada, who is retiring.

That the Democrats are favored in this election should not be surprising.

The 2016 Senate elections boded well for the Democrats without any consideration of a possible Trump effect on down-ballot races. In recent history, Democrats have done better in presidential election years than in midterm years, when turnout is lower. Most of the senators up for re-election last went before the voters in the Republican wave election of 2010 — when the G.O.P. made big and broad gains in an anti-Obama environment — leaving Republicans with several potentially vulnerable incumbents.