Special counsel Robert Mueller apparently hasn’t found any evidence to convict Trump officials of “colluding with the Russians” to throw the 2016 presidential election, so he’s issued a new subpoena to former Trump campaign officials.

The subpoena orders them to hand over Russia-related documents and emails that contain certain keywords relating to the investigation.

A source told the Wall Street Journal that Mueller’s team has asked more than a dozen top campaign officials to submit documents and emails that reference a set of Russia-related keywords, according to an unnamed source. The subpoena did not compel any officials to testify before Mueller’s grand jury, the person said.

The subpoena caught the campaign by surprise, according to the WSJ report. The campaign had previously been voluntarily complying with the special counsel’s requests for information and had been sharing with Mueller’s team the documents it provided to congressional committees as part of their probe.

Separately, on Thursday, the Senate Judiciary Committee said senior White House official Jared Kushner hadn’t turned over all the documents it has requested and asked his lawyer to be more forthcoming.

Congressional committees earlier this year asked the campaign to turn over Russia-related documents, emails and phone records dating back to June 2015, when Trump launched his campaign.

According to the report:

Sending a subpoena to an entity that says it has been cooperating with document requests isn’t unusual in cases in which prosecutors have some concern that their demands aren’t being met promptly or aren’t being entirely fulfilled, former prosecutors said. A subpoena can serve as a backup, to make sure the recipient is complying as promised, and as a reminder that failure to provide documents as demanded would count as obstructing a grand-jury investigation.

Trump officials have been handing over the requested documents on an “ongoing” basis, the source added.

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