On June 6, the Federal Election Commission filed this in the U.S. Supreme Court in National Republican Senatorial Committee v FEC, 24-621. The FEC says it supports the Democratic Party’s desire to intervene in the case, which is about the federal law that prohibits parties from spending much money in support of their own nominees if the party and the candidate are coordinating with each other.
Both the Republican Party and the FEC agree that the limits on such party spending violate the First Amendment. But if the U.S. Supreme Court is to take the case, there needs to be some organization that will defend the federal limits. The Democratic Party wants to defend the limits, so letting the Democrats into the case at this late point would facilitate that.
It is somewhat strange that the Democratic Party wants to defend a law that injures political parties.