The seven Senate seats most likely to flip

Republicans are looking for opportunities to go on offense in their battle for the Senate majority and stunt the momentum Democrats have built over the course of the summer.

But Democrats, fresh off a season of eyepopping fundraising and legislative wins, aren’t taking their rose-tinted summer for granted as Republicans ramp up spending in key states and tailor their general election messaging.

Seven weeks before Election Day, Senate races in closely watched swing states remain tight, but a clearer picture is beginning to emerge of the landscape heading into the...