Divergence between branches makes the threat credible.

We also argue that our assessment of competing accounts should consider lawmakers’ calculations about the likelihood their messaging behavior leads to change on the part of the Court. In other words, individual lawmakers may Court curb in order to send messages to the Court itself, attempting to affect its behavior. Our reasoning here is rooted in the calculations that members of the majority make about the value of sending a message to the Court. We argue that members of the majority have a stronger incentive to Court curb when their party is distant from the Court because their proposals, as opposed to ones from the minority party, are more likely to reach the floor (Anderson, Box-Steffensmeier, and Sinclair-Chapman 2003; Cox and McCubbins 2002).6 Since the Court is particularly concerned about attention-generating proposals, which spark widespread backlash against the institution (Clark 2011, 77), majority-initiated proposals represent more credible threats to the Court's support due to majority-party agenda control. In other words, members of the majority party have an additional incentive to ramp up their threats against a distant Court because the judiciary sees threats from the majority as more credible, making it more likely that it will adjust its behavior as a result. We posit that majority-party members are comparatively more likely to Court curb than minority members when their party is distant from the Court due to the fact that the institution perceives these majority threats as more credible.

For example, in 2006, Congress made a highly credible threat against the Court: it passed a piece of Court-curbing legislation that stripped the federal judiciary of jurisdiction over writs of habeas corpus for “enemy combatants” in the War on Terror. This effort was spearheaded by Senate Majority Whip Mitch McConnell, reached the floors of both chambers, and passed overwhelmingly by majority-party Republicans in the House and Senate. Because McConnell's party held preferences that were moderately distant (i.e., more conservative) from the Roberts Court, our logic suggests that McConnell would be more likely to forward Court-curbing legislation than if he were a member of the minority party, all else equal. This is because a member of the majority party is likely to see additional value in sending a message to the Court since he perceives the proposal as a viable signal to the Court of a potential institutional curtailment, rather than solely a signaling device to his constituents. Therefore, we anticipate that when the Court is distant, majority-party members see additional value in Court curbing and are thus more inclined to offer such proposals than their minority-party counterparts.7