WASHINGTON — The Supreme Court’s conservative majority on Monday sided with Republican Sen. Ted Cruz of Texas in his challenge to a provision of federal campaign finance law, in a ruling that a dissenting justice said runs the risk of causing “further disrepute” to American politics.The justices, in a 6-3 decision that divided the court along ideological lines, agreed that the somewhat obscure section of the law violates the Constitution. The decision comes just as campaigning for the 2022 midterm …