Thursday, September 26, 2013

States of Change

Not long after the 2012 election some observers noted an increasing Democratic "lock" on the Electoral College. Although Republican nominee Mitt Romney's campaign took a lot of heat for losing election, there has developed a general sense that changing demographics in key states are setting the stage for continued Republican difficulties in years to come. By this account, increasing numbers of Latino and Black voters--both heavily Democratic groups--in some areas have moved enough states to the Democratic column that Republican presidential candidates face an uphill battle in anything other than a bad Democratic year.   And there is every reason to expect this demographic trend to continue. This idea has gained enough currency that some Democrats even see Texas, with its increasing Latino population, turning blue at some point in the future.

My interest here is in documenting the changes party fortunes in the states and trying to get a sense of which changes are of greatest consequence to the race to 270.  Of course, I am not only interested in where Democrats have strengthened their position but also where they have lost ground to Republicans; for there are clearly parts of the country where Democratic prospects have dimmed appreciably over time.

I use state-level presidential election returns from 1972 to 2012 to document the trends in party support. The starting date for this type of analysis is somewhat arbitrary, but using 1972 puts us on this side of the beginning of partisan changes in response to party strategies related to civil rights.  I focus on the trend over time in the centered (around the fifty-state mean) Democratic share of the two-party vote, separately for each state.  Centering the vote allows me to focus on each state relative to all other states without worrying about overall swings in party fortunes from one election to the next.  So the focus is not on which party wins or loses a state, but on support for the Democratic party over time in a given state,  relative to all other states.  To gauge the trend over time I regress vote share on year, separately for each state, and also included dummy variables for presidential and vice-presidential home state advantage, as well as one for southern states in 1976 and 2000.  The southern dummy variable is necessary to capture the unnaturally high level of support for the Democratic ticket in the south in response to the candidacy of former Georgia Governor Jimmy Carter.  I then used the results from the state-by-state regression models to estimate the trend in Democratic support over time.  In doing this I set the values for the dummy variables to zero so the "predictions" reflect the trend over time exclusive of these transitory perturbations.

The figures below document the changes in Democratic fortunes.  In each figure, the solid straight line represents the estimated trend in Democratic support over time, and the points represent the actual election outcomes.  It is important to recall that in some cases the trend line does not appear to fit the scatter plot as well as it "should" because it excludes the effects of home state advantages and the southern advantages in 1976 and 1980 (see MS and GA as exemplars of this phenomenon).  It is also worth pointing out that the observations above the zero point (dashed line) are not necessarily cases in which the Democratic candidate won the state; instead, these are cases in which the Democratic candidate fared better than he did, on average, across the fifty states.

The panel of graphs below displays the pattern of partisan change among those twenty-five states in which the Democrats have seen their greatest gains, ordered by magnitude of gains from upper left (across rows) to lower right.  These states generally fall into four different categories.  First there are those states that moved from somewhat competitive to favoring the Democratic candidate: California, Delaware, Connecticut,  Hawaii, Illinois, Maine, Maryland, New Jersey, New Mexico (very slightly), New York, Vermont, and Washington.  Some of these states leaned slightly Democratic in the early 1970s while others were truly toss-up states; but almost all of them have moved comfortably into the Democratic column.  These changes represent an important net gain for the Democratic party. As a group, these states comprise 166 electoral votes that the Democrats can count on now much more confidently than they could forty years ago.

Twenty-Five States with the Greatest Democratic Gains 
in Presidential Elections from 1972 to 2012

Another important group consists of those states that moved from tilting Republican to being truly competitive: Colorado, Florida, New Hampshire, Nevada, and Virginia.  To be sure, these are not states that the Democratic candidate can count on--they are, after all, competitive--but they are states that used to be much farther out of reach for the Democrats and now are up for grabs.  Together these states comprise 61 additional electoral votes in states that have moved toward the Democratic party.

Finally, we have states that were strongly Democratic and became even more so (Massachusetts and Rhode Island), and several states where the change was either very slight and didn't alter the general outlook for either party (Arizona, Georgia, and Mississippi), or that can best be described as flat-liners, impervious to whatever process has driven the changes in other states (Michigan, Oregon, and South Carolina).  Technically, there has been some change in this latter group of states but it is so slight that it is barely discernible in these plots.

Of course, not all states have trended so favorably toward the Democrats.  The panel of graphs below illustrates the pattern of party change in the remaining states, where Democrats either lost  ground to Republicans or just managed to hold their own.  One state that stands out here is West Virginia, which has shifted from a place where the Democratic candidate typically ran ahead of his performance across the other forty-nine states to a place that now appears to be a long shot for Democratic candidates.   Minnesota is another interesting state.  Although the Democratic candidate continues to fare slightly better in Minnesota than in the rest of the country, there has been a very gradual decline in that advantage.  Democrats continue to win there, but Minnesota is somewhat more competitive now than it was thirty or forty years ago.

Probably the most consequential set of states in this figure are those that have moved from being somewhat competitive to being out of reach for the Democratic candidate: Arkansas, Kentucky, Louisiana, Montana, South Dakota, Tennessee, and Texas (so much for Texas turning Blue--see above).   In strong Democratic years, they were once possible pickups for the Democrats, but they now appear to be out of reach.  As a group these states, along with West Virginia and Minnesota,  constitute 92 Electoral Votes. 

Twenty-Five States the Greatest Democratic Losses (or smallest gains)
in Presidential Elections from 1972 to 2012

Of course, there are a number of states that were fairly Republican in the early 1970s and have become more so over time: Alabama, Alaska, Idaho, Kansas, North Dakota, Oklahoma, Utah, and Wyoming.  And there is also another group of flat-liners, which includes states with very, very slight Democratic decline (Indiana, Missouri, Nebraska, North Carolina, and Wisconsin), and a group with almost imperceptible Democratic gains (Iowa, Ohio, and Pennsylvania).   These states (flat-liners and Republican states that became more Republican) don't really have much of an impact on the on the partisan advantage in the Electoral College.

While the figures above provide a lot of state-by-state detail, the same information can also be summarized using a heat map and the by-now-familiar Red/Blue schema.  The interactive map pasted below shows how states have changed over the the last forty years. 

Changes in the Centered Democratic Share of the Two-Party Vote in U.S. 
Presidential Elections, 1972-2012
(Blue=DemocraticAdvantage, Red=Republican Advantage)

In keeping with data already presented, the dominant patterns over time are purplish states turning blue, followed by fewer purple states turning red, some reddish states turning even redder, and a number of reddish states turning purple.1

The movements over time have clearly favored the Democratic Party. Those states that have moved from somewhat competitive to Democratic, or from leaning Republican to fairly competitive, combine for a total of 227 electoral votes. Among those states that have made similar shifts toward the Republican Party (other than those that were in the Republican column to begin with), the electoral vote count is only 92. Perhaps the worst news for the Republican party is that there is only a single large state that has moved in their direction: Texas, which has gone from leaning slightly Republican to being a strong Republican state. Contrast that with the Democrats, who have seen California, Illinois, New Jersey, and New York move from somewhat competitive to strongly Democratic, and Florida has moved from leaning Republican to very competitive.

Still, there is nothing resembling a "lock" on the Electoral College.  A clear trend toward the Democratic Party, yes, but hardly a lock on anything.
Erratum (September 2014):  There was an error in estimating the slope for North Carolina (control for Carter's southern advantage in 1976 and 1980 was not included).  When that error is corrected, North Carolina emerges as another state in which the Democrats have made smallish gains.  See the updated figure here.
1I think. I'm color blind, so this may look a bit different for you.