I want to clarify my claim last night that Republicans in Congress will not dramatically shift their voting patterns in response to a perceived Obama mandate. A friend correctly pointed out to me by email that a mandate response isn't necessary for Obama to change the legislative status quo. What mattters is the configuration of the veto and filibuster pivots in Congress.
The simplest way to understand what legislation gets enacted is a one-dimensional model popularized by Keith Krehbiel, David W. Brady, and Craig Volden. As I've noted before, we can imagine a single left-right dimension of ideology with all the members of Congress and the president represented as points on that dimension. The gridlock zone represents the ideological range defined by the filibuster and the veto.
We can use this simple model to illustrate the effect of the 2008 election. In the current Congress, the gridlock zone is the space between the 41st most liberal senator (the filibuster pivot) and the 67th most liberal senator and 290th most liberal House member (the veto pivots). Assume that we can also locate the ideological content of policies on this dimension. We can show that any status quo policies in that range cannot be altered -- a move to the right will be blocked by the filibuster pivot, and a move to the left will be blocked by a presidential veto that the veto pivots will not override.
In the next Congress, two things will happen. First, the configuration of the zone flips. Now Obama is to the left of the gridlock zone rather than to the right. As a result, the zone runs from the 33rd most liberal senator and the 145th most liberal House member (the veto pivots) to the 59th most liberal senator (the filibuster pivot). Second, the composition of Congress has shifted to the left as a result of the defeat of moderate Republicans and the election of more Democrats. As such, the the 33rd most liberal senator, the 145th most liberal House member, and the 59th most liberal senator are likely be to the left of their counterparts in the current Congress.
To illustrate, the previous veto pivots on policy shifts to the left were (approximately) Lamar Alexander (R-TN) and Joseph Knollenberg (R-MI). These members (or close equivalents) could block any proposal to the left of their preferred point on the ideological spectrum by supporting a Bush veto that would therefore not be overriden.
In the next Congress, however, the relevant constraint will be the 59th most liberal senator. Assuming that new Democratic senators will be to the left of Nebraska's Ben Nelson (the most conservative Senate Democrat), the filibuster pivot will be Nelson if Democrats win two of three outstanding seats in the Senate, Olympia Snowe (R-ME) if Democrats win one, or Susan Collins (R-ME) if Democrats win no additional seats. Any status quo policy located between Nelson and Alexander can now be moved far enough to the left to make Nelson indifferent between the status quo and the current policy.
This shift frees up S-CHIP expansion and other bills Bush vetoed as well as issues such as health care and energy that are key priorities for Obama. And if Democrats use the reconciliation process to bypass the filibuster on health care, the relevant constraint shifts all the way to the 50th most liberal senator (since Biden can break the tie). Obama may be able to pass a great deal of important legislation without a perceived mandate.
Update 11/10 2:01 PM: Rob correctly points out in comments that Bush's stem cell policy can be reversed by executive order, so I've removed it from the list of policies that can now pass Congress (Bush vetoed a bill that would have overturned his executive order).
With respect to federal funding of embryonic stem cell research, my understanding is that the current restriction on funding (to then-existing stem cell lines) was imposed by Executive Order. Congressional attempts to overturn that restriction have been unsuccessful, but all that's required to reverse the Executive Order is a new Executive Order. If I'm right, this is one issue you can take out of the hopper for necessary Congressional action.
Posted by: Rob | November 10, 2008 at 01:59 PM