Will Democrats Win Back the Senate?

We are a bit less than a year away from the 2016 presidential election, and one of the major parties, barring some unlikely legal developments, appears to have settled on its nominee. Hillary Clinton will almost certainly be the Democratic Party standard-bearer next November. The Republican race is remarkably unsettled. Two newcomers to politics, businessman Donald Trump and pediatric neurosurgeon Ben Carson, continue to lead all GOP polls, drawing 45-50% of the vote between them in most surveys.

Most analysts believe both candidates will fade, and the eventual nominee is likely to be one of two Cuban American senators: Marco Rubio of Florida or Ted Cruz of Texas. Both Rubio and Cruz have seen their poll numbers rise, both nationally and in the early states, to 10% or more, but their gains have been primarily at the expense of others in the vast Republican field of contenders, rather than Trump or Carson.

In early tests of a general election contest between Hillary Clinton and the leading Republicans, Carson and Rubio score better than Trump and Cruz.

The general election polls are all over the place, however, with some showing Clinton behind almost all Republicans, and others showing her ahead of everyone but Carson.

The presidential election race matters for the battle between the parties for control of the U.S. Senate as well. In the midterm elections of 2014, Republicans picked up nine seats: seven wins came in states that Mitt Romney carried in 2012, and two -- Iowa and Colorado -- came in states Obama won that year.

The GOP picked off five Democratic incumbents in 2014, in Alaska, Louisiana, North Carolina, Arkansas -- all states won by Romney -- as well as Colorado. Republicans won open-seat races in four states, three Romney-carried states -- Montana, West Virginia, and South Dakota -- plus Iowa.

In general, picking up seats in open-seat races is easier than knocking off incumbents. Romney won six of the seven states listed above by sizable margins -- only North Carolina was very competitive (a 2% Romney margin). Republicans also came close to picking up two more seats from incumbent Democrats in 2014 -- in Virginia (1% victory for Mark Warner), and New Hampshire (a 3% win for Jeanne Shaheen).

The 2016 Senate map appears very favorable to Democrats. The Democrats now hold 46 Senate seats, and need a net gain of four to win Senate control, assuming Clinton is elected, or five if a Republican wins the White House. Twenty-four of the 34 Senate races in 2016 are in states where Republicans now hold the seat. In seven of these states -- Illinois, Wisconsin, Ohio, Florida, Pennsylvania, Iowa, and New Hampshire -- Obama won the state in 2012.

Next year’s Senate contests are obviously taking place in a presidential election year. This generally means stronger Democratic turnout than seen in off-year races, such as in 2010, when the current Republican senators in these states were elected to all of these seats for the first time, except for Iowa, where Chuck Grassley has long served and is expected to win easily in 2016. However, unlike the 2014 Senate contests, when Republicans were aiming for gains in states won by Romney by big margins in 2012, the Republican-held seats in Senate races next year in the seven states carried by Obama in 2012 were much more closely contested in the presidential election in 2012, except for Illinois, which Obama won handily.

Over the last few cycles, in both midterms and presidential election years, one or the other party has won most or all of the closely contested races. Pundits like to use the term “drawing to an inside straight” to suggest the difficulty for one party to win such a high share of the close races. Based on the recent history, pulling an inside straight is far more common in U.S. elections than at the poker tables. Assuming Hillary Clinton wins a close race for the presidency, her party has a good shot at picking up the net four seats it needs to win back the Senate, but it might also wind up a seat or two short. 

If Republicans nominate a wild-card candidate, such as Trump, who is then beaten soundly in the general election, Democrats might win far more than a net of four seats. If Republicans win a close race for the White House, their chances of retaining control of the Senate are better than 50-50, in part because Democrats then need to pick up a net of five seats.