Sen. Bernie Sanders, I-Vt., sent the Democratic National Committee a fat check in May, according to a report Wednesday.

The former candidate for the Democratic presidential nomination donated $100,000 to the DNC in order to cover the costs of traveling the country with DNC Chairman Tom Perez over the past few months, Politico reported.

Last summer, WikiLeaks published stolen DNC emails showing that then-DNC chair Rep. Debbie Wasserman Schultz and other DNC officials worked to undermine Sanders in favor of his primary opponent Hillary Clinton. The ensuing controversy forced Wasserman Schultz to resign. Sanders also sued the DNC in late 2015 in federal court to regain access to Democratic Party voter data, claiming that there was a breach of contract. Sanders withdrew the lawsuit in 2016.

As part of an effort to lessen tensions within the party, after the more establishment-favored Perez was elected the new chairman in February, he chose the progressive Sanders backer Rep. Keith Ellison, who lost to Perez in the DNC campaign, to be his deputy chair.

Sanders took part in a nine-state "unity tour" with Perez earlier this year, but the senator has remained critical of the Democratic Party, saying earlier this month that the party needs to go through "fundamental" changes in order to stop losing elections.