WASHINGTON — In Michigan, an ad attacking Terri Lynn Land, the Republican candidate for the United States Senate, opens with a shot of rising brown floodwaters as a woman says: “We see it every day in Michigan. Climate change. So why is Terri Lynn Land ignoring the science?”

In Colorado, an ad for Cory Gardner, another Republican candidate for Senate, shows him in a checked shirt and hiking boots, standing in front of a field of wind turbines as he discusses his support for green energy.

And in Kentucky, a spot for the Republican incumbent Mitch McConnell, the Senate minority leader, depicts him flanked by coal miners as a woman intones, “The person fighting for our coal jobs is Mitch McConnell.”