Rep. Joe Donnelly (D-Ind.) received a surprise in his mailbox last week.

Six-term Sen. Dick Lugar (R-Ind.), who faces the toughest primary challenge of his career on May 8, sent the likely Democratic Senate nominee’s “household” a piece of his own campaign mail.

The mail piece, provided by the Indiana Democratic Party, emphasized that Lugar wants to repeal “Obamacare” and “cut spending.” There’s an application to vote absentee in the upcoming primary attached to it.

But on the whole, it’s a relatively nonpartisan mailer for a primary, especially given Lugar is running in a highly competitive GOP primary against state Treasurer Richard Mourdock. Just last week, an independent poll showed Lugar leading Mourdock by a mere 7 points with the help of GOP-leaning independents in Indiana’s open primary.

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So is Lugar targeting Democrats to cross over to vote for him in the primary?

Lugar’s campaign spokesman, Andy Fisher, denied that. Fisher wrote in an email that either “someone in the Donnelly household voted in a Republican Primary in the last couple cycles” or “the list vendor picked up some bad addresses.”

A spokesman for the Indiana Democratic Party countered that Donnelly and his “household” only voted in Democratic primaries in recent cycles, according to its internal voter files.

Campaigns and direct-mail consultants often scrub their address lists for opponents and media. But it’s not uncommon for an opponent to receive campaign pieces like Lugar’s mail.

One GOP direct-mail consultant even said they like to send their mail to the opponent for a reason.

“It always gets in their head,” the consultant said.