Their videos have proliferated on social media, but the payments are frequently hidden from viewers.

Relatives of a family killed by a semi truck say they were not consulted about the ad, which connected the crash to illegal immigration.

The pro-Israel group has been preparing to spend big for Mike Rogers, the Republican nominee for Senate in Michigan. Does he want that?

© Paul Sancya/Associated Press

With opposition to the centers mounting, many Democrats and a growing number of Republicans are campaigning against them.

© Aubrey Trinnaman for The New York Times

Aisha Wahab, a Democratic state senator in California, will fill out the term of Eric Swalwell, who resigned from the House amid accusations of sexual misconduct.

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A burst of ad spending is part of a campaign tactic in which the major parties try to boost fringe hopefuls on the other side.