WASHINGTON — In a remarkable slap at their own presidential nominee, Republicans are running a TV ad in Chicago that touts a GOP congressman’s independence by showing him saying Donald Trump ‘‘has disqualified himself.’’
The spot is aimed at helping Illinois Rep. Robert Dold, considered one of Congress’ most endangered Republican incumbents in the Nov. 8 elections. His district in Chicago’s northern suburbs is heavily Democratic, having backed President Barack Obama with 58 percent of its vote in 2012 and 63 percent in 2008.
The ad is by the National Republican Congressional Committee, the House GOP campaign organization that is spending tens of millions of dollars to back the party’s candidates around the country. An NRCC official declined to comment on the spot.
While Trump’s presidential campaign has faltered in recent weeks, the ad marks the first time the committee has used a message openly criticizing the party’s own presidential candidate.
‘‘Dold is an independent voice who stood up to Donald Trump months ago,’’ the narrator says.
The ad then shows Dold saying in a television interview, ‘‘Listen, I think Donald Trump has disqualified himself.’’
Several GOP ads have promoted congressional candidates as curbs against the policies that Democrat Hillary Clinton would favor as president — an implicit acknowledgment that Trump will lose. It’s unusual for a party to adopt even that tactic, and far more so for it to highlight one of its own candidates lambasting its presidential contender.
The NRCC is spending around $1.1 million on the ad, which began airing Tuesday on broadcast and cable TV stations in Chicago and is expected to run about a week. The figures were provided by people with access to political advertising data who spoke on condition of anonymity because they were not authorized to discuss the information publicly.
Dold, in his second term, is embroiled in a rematch against former Democratic Rep. Brad Schneider. The ad says Schneider has shown ‘‘no independent leadership.’’
Democrats seem certain to gain House seats on Election Day, but Republicans are expected to retain a majority in the chamber. It would take a 30-seat gain for Democrats to capture control, a huge pickup.