How the Senate map shift helped Trump win acquittal

WASHINGTON — Donald Trump’s second impeachment trial followed a very predictable partisan path in the U.S. Senate last week, with Democrats voting to convict and most Republicans voting to acquit. There is a long list of reasons behind that breakdown, but one of them is the increasingly tidy alignment between the Senate and the presidential partisan maps.

It used to be that many states featured divided Senate delegations, and that presidents won the vote in states represented by the opposite party in Congress’ upper chamber. But that pattern has been in decline for decades now. And it’s advanced to the point where today, in 2021, the presidential election and Senate maps look remarkably similar.

You can get a sense of the change by going back to 1993, when President Bill Clinton came to Washington after 12 years of Republicans in the White House. Clinton won 32 states in the 1992 election and those states held a lot of partisan diversity in the Senate.

Just under half of the states he won, 15, were represented by entirely Democratic delegations. Three of the states he won were represented by entirely Republican delegations. And close to half, 14, were represented by split delegations: one Democrat and one Republican.

In those Republican and split states, that meant the senators from the opposing party were answering to voters who also had just elected a Democrat to the White House. There was some impetus to try and reach out to work together — or, at least, to feign working together.

In addition, there were three states with Democratic Senate delegations that did not vote for Clinton. The point is that the partisan line was blurrier back then, but it has become much clearer in the years since.

When Barack Obama won the White House in 2008, he carried 28 states and there was a noticeable increase in the partisanship of that coalition of states in the Senate.

Two-thirds of the states Obama won, 19 of them, were represented by two Democrats in the Senate. One state that voted for Obama, Maine, was represented by two Republicans. And eight of the states that voted for him were represented by split delegations.

In addition, there were four states with Democratic Senate delegations that did not vote for Obama. Those states — Arkansas, West Virginia, Montana and North Dakota — were on their way to taking on a more Republican cast. Six of those states’ eight senators are now Republican.

The net impact was that Obama had to lean more heavily on purely Democratic group of senators. He simply held less electoral sway over Republican and split delegations.

But those numbers still look relatively bipartisan compared to where we are in 2021. The 2020 presidential results line up almost perfectly with the partisanship of the current Senate delegations.

President Joe Biden won 25 states on his way to the White House and 22 of them hold Democratic Senate delegations. The other three come from states with split delegations. None come from states with Republican delegations.

That probably limits the power of Biden’s presidential bully pulpit to sway the other side in the Senate. It also suggests some of the reason about why we saw such loyalty to former President Donald Trump in last week’s impeachment trial. The overwhelmingly majority of Senate Republicans — all but three — come from states that voted for Trump.

One thing you’ll notice when you look at all the numbers here is that the Democratic wins in Republican states have shrunk considerably and consistently since Bill Clinton. Some of that has to do with shifts in the politics of those states. It seems remarkable, for instance, that Oregon had two Republican senators in 1993 (or that Alabama had two Democrats).

But the other sharp decline in these data comes in these presidents winning states with split delegations. And that has less to do with these presidents being able to appeal to “split states” than it does with the fact that there just aren’t many states with split delegations anymore. Split Senate delegations have become an endangered species in American politics.

In 1993, Clinton’s first term in office, close to half the states in the country had split delegations. By George W. Bush’s first term, the number was 14. It was 13 states for Obama’s first term and 12 for Donald Trump’s term. Currently, there are only a half dozen states with split Senate delegations.

That means when a new president arrives in town and hopes to craft an agenda, he immediately is dealing with a Senate where the partisan divisions are stark and where there is most likely little motivation for compromise. It also means you are more likely to get the very partisan story we saw in the impeachment trial this past week.

To be clear, none of this means that the behavior that currently defines the Senate is “wise” or “good for politics,” but isn’t irrational either, considering the divides running through the country. Over the last 30 years the voters have spoken, and they have created a deeply partisan body on Capitol Hill.