Will the addition of Brett Kavanaugh to the US Supreme Court change the Democratic and Republican parties’ ideas about the power and place of the federal judiciary in American life? The theory presented in this chapter predicts that it will. Examining American history from the Marshall Court to the Roberts Court, this chapter finds that change in party control of the Supreme Court can help explain change in party ideologies with respect to judicial intervention. Parties in long-term control of the Supreme Court tend to change their ideology in ways that call for judicial supremacy and judicial activism, while parties in opposition tend to change their ideology in ways that call for judicial deference to the elected branches of government.