President Donald Trump said Monday that the Justice Department will "pretty soon" file a federal lawsuit aimed at blocking California’s newly approved congressional redistricting plan. Speaking to reporters at the White House, Trump predicted the administration would "be very successful" in overturning the measure, which he branded a partisan gerrymander. The Democratic-controlled California legislature last week passed—and Governor Gavin Newsom promptly signed—legislation placing a revamped congressional map on the Nov. 4 ballot. Supporters say the changes, proposed after Texas adopted a Trump-backed map favorable to Republicans, could shift as many as five U.S. House seats toward Democrats. Newsom responded to Trump’s threat on social media with a terse "bring it." Even before Trump’s remarks, California Republicans filed an emergency petition with the state Supreme Court on Monday, their second legal challenge in a week. The suit argues that the legislature’s action violates a state constitutional requirement that political boundaries be set by an independent redistricting commission. An earlier lawsuit was dismissed by the court last week. Trump also signaled he may sue over the Senate’s century-old "blue slip" custom, which lets home-state senators block judicial and U.S. attorney nominees. Judiciary Committee Chairman Chuck Grassley, a longtime Trump ally, defended the practice, noting it helped Republicans block dozens of Democratic nominees when Joe Biden was president. Trump contends the tradition is "unconstitutional" and is hindering confirmation of nominees such as Acting U.S. Attorney for New Jersey Alina Habba.