Are federal elections in the US inherently likelier to be Republican than Democratic victories?

[Vosem]

epistemic status: 70% serious, 30% kidding, but the data does add up

America has two kinds of elections that the entire country participates in simultaneously: presidential elections and House elections. People tend to vote similarly in both kinds of races and only rarely split their ballots for exceptional candidates (even if they support a different party at the state level). Since 2000*, Republicans have won these elections more often than Democrats:

Republican victories (11): 2000-House, 2000-POTUS, 2002-House, 2004-House, 2004-POTUS, 2010-House, 2012-House, 2014-House, 2016-House, 2016-POTUS, 2022-House
Democratic victories (7): 2006-House, 2008-House, 2008-POTUS, 2012-POTUS, 2018-House, 2020-House, 2020-POTUS

11 to 7 is a pretty decent advantage. If you shift these results to popular vote, though, something different emerges:

Republican victories (8 ): 2000-House, 2002-House, 2004-House, 2004-POTUS, 2010-House, 2014-House, 2016-House, 2022-House
Democratic victories (10): 2000-POTUS, 2006-House, 2008-House, 2008-POTUS, 2012-House, 2012-POTUS, 2018-House, 2020-House, 2020-POTUS

Democrats now win, but it's 10-8 -- a slightly smaller advantage. (If you literally average all these elections out, then you get an average result of ~D+1).

My question is -- are Republicans just inherently more likely to win national elections in the US? If we are forecasting a national election, should we say that there is roughly a ~60% chance that it will be a Republican victory before any campaigning happens? (And a similar roughly ~60% chance that it will be a Democratic popular vote victory, perhaps?)

(There is a distinction here between presidential races and House races, but it mostly shows up in the popular vote, where presidential races are 4-1 D while House races are still 7-5 R. Using actual winning, you have a 3-3 tie presidentially while House races are 8-4 R. Is there a reason Republicans should do better in House races and Democrats in presidential races? When we hold elections concurrently, the pattern is a little weak -- House Republicans did better than their presidential candidate in 2000/2012/2016/2020, but worse in 2004/2008.)

^{*This is an arbitrary cut-off, but it doesn't really matter where you put it; if you go backwards, you hit a tie in 1978 and a Democratic advantage in 1976. If you move forward, you get Democratic advantages in 2006/2018/2020, and ties in 2008/2016; for most starting years the result is roughly the same.}