Brad Parscale said in a statement that he is “unaware of any Russian involvement” in the data and digital operations of Trump’s campaign. He said he is voluntarily appearing before the panel and looks forward to “sharing with them everything I know.”

Rep. Adam Schiff, the top Democratic on the House Intelligence Committee, says lawmakers are reviewing whether Trump campaign’s team worked with Russians in any way, including to distribute “fake news.”

“We are very interested in finding out whether there was an effort to make use of data analytics—whether there was Russian funding or support for that, or Russian assistance in any way with gathering data that could be used by the campaign or any associates of the campaign,” Schiff said last month in an interview on MSNBC.

Parscale is a key figure in that part of the probe.

He’s close with the Trump family, having worked on websites for the Trump Organization and Ivanka Trump’s company since 2011. Parscale and Jared Kushner, Trump’s son-in-law and senior adviser, pushed Trump, a political newcomer, to embrace data—an aspect of modern campaigns that Trump had disparaged as “overrated.”

The Trump campaign paid Parscale’s San Antonio, Texas-based firm more than $90 million to advertise on social media, analyze data and perform other campaign functions.

He said the campaign “used the exact same digital marketing strategies that are used every day by corporate America.”

Through Parscale, the campaign paid dozens of data and digital specialists to work out of the San Antonio office of Giles-Parscale. Major technology companies including Facebook, Twitter and Google detailed employees to work “side-by-side” with the campaign operatives, Parscale said.

Companies often detail representatives to major advertisers, and those three offered the same services to Clinton’s campaign. Facebook said in a statement the company has been in touch with several lawmakers who are interested in the subject.