CNN  — 

It’s often been said that President Donald Trump is “underperforming the fundamentals”. Some believe Trump’s doing worse than the average Republican president would be doing in the polls under similar circumstances. It’s difficult to prove that, however.

But at least one key indicator suggests Trump is, indeed, doing worse than the average Republican would be doing in the same conditions – Trump doesn’t seem to be receiving the average boost an incumbent does compared to his party brethren in the House.

Look at the live interview polls (and all surveys, for that matter) taken this summer that asked about race for the presidency and the race for Congress. Counting each pollster only once in the average, former Vice President Joe Biden leads Trump by 10 points in these polls. Democratic House candidates are ahead of the Republicans by 8 points on the generic congressional ballot in these same surveys.

This goes in tandem with the fact that Republican candidates for the House are less likely than Democratic candidates to release internal polls that include a presidential result. In theory, this would indicate that Trump is weak in their districts.

The fact that Biden’s lead is wider than the House Democrats’ edge is unusual. If it holds, it would be historic.

You’d expect that Trump would be doing better than Republicans running in the House. The simple reason is that more Democrats (i.e. the majority party) have an incumbency advantage in the House, while Trump enjoys that same advantage for the presidency.

Historically, incumbents have done very well against challengers. We see that in races for all levels of office (e.g. House, Senate and president). Incumbent presidents have gone 10 for 13 in their bids for another term in the last 80 years. And even as the incumbency advantage has declined in the House, it’s still worth about 3 points.

View Trump and Biden head-to-head polling

Since 1940, there have been eight elections where an incumbent president was running for another term and his party did not control the House. In these elections, the president has done better than the members of his party running for the House six of eight times (75%). The president has never underperformed his House counterparts by more than 3 points in any of these years.

We saw the phenomenon occur as recently as 2012. Then-President Barack Obama won the popular vote by 4 points, while House Democrats, who were in the minority, only won the House popular vote by 1 point. In other words, Obama outperformed the House Democrats by 3 points.

Of course, eight elections is not a particularly large set of elections. We can widen it out to include the elections where the incumbent president was not running for another term. In these cases, we should still expect the party that controls the majority in the House to do better in House races than it does in the presidential race because incumbents do better.

If we include these elections in our group, the party with House control has outrun their party’s presidential candidate 13 of 15 times (87%) in the last 80 years.

Or put another way, the minority party in the House has done better in the presidential race 13 of 15 times when they either control the White House or the incumbent president is not running for re-election. The vast majority of the time, it’s not even close.

In elections where the House minority either controls the White House or an incumbent is not running for re-election, the House minority party has done better in the presidential race by 3 points or more (rounded) 12 of 15 times (80%) in the last 80 years. Trump right now is 5 points below this threshold, as he is underperforming House Republicans by 2 points.

Interestingly, the generic congressional ballot has remained fairly steady for most of 2020. Trump was doing better than House Republicans for much of the year, until this summer.

Now, it could be the case that House Republicans are running ahead of Trump because voters are intentionally splitting their ticket. It’s possible that they believe Trump will lose, so they don’t want to give Democrats full power. Voters, though, are slightly more inclined to believe that Trump will win re-election than lose it.

This suggests that Trump was hurt by probably two issues: his handling of the coronavirus pandemic and race relations. The coronavirus pandemic has gotten worse this summer, while race relations were brought to the news late this spring after the killing of George Floyd.

Trump’s approval rating on the coronavirus and race relations is in the 30s. Voters may be blaming him for his response without passing on the penalty to House Republicans.

Perhaps the good news for Trump is that if he is doing worse than the fundamentals, then he has room for improvement without the political environment changing too much.

Of course, even if Trump was doing as well as Republican candidates for the House, he would still be trailing.