(CNN)It's nothing new to say that members of the Democratic Party and the Republican Party don't see eye to eye. After all, there's a reason they belong to different political parties.

       But over the last few years, it really does seem that the dislike between the two sides has hit another level. Witness this week in Congress, when GOP Rep. Paul Gosar of Arizona was censured for, as my colleagues Annie Grayer and Clare Foran put it, "posting a photoshopped anime video to social media showing him appearing to kill Democratic Rep. Alexandria Ocasio-Cortez and attacking President Biden."

       The Gosar episode is part of a larger trend in American politics of tribalism and one side seeing the other as the enemy -- though as much as House Republicans accused Democrats of hypocrisy in the debate over Gosar's censure, none of them pointed to a comparable moment in which a Democratic member had depicted the murder of a Republican colleague.

       The percentage of Americans who strongly dislike the opposition party has gone up by about 400% in just the last two decades.

       You can see this very clearly in the numbers. Take a look at the American National Election Studies. Since the late 1970s, they have been asking Americans to regularly rate on a scale of zero (very cold) to 100 (very warm) how they feel about each political party.

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       In 1978, Democrats and Republicans were actually pretty OK with the other party. The average Democrat rated the Republican Party a 48, as in right in the middle. The average Republican rated the Democratic Party at a similar 46.

       Even as late as 2000, respondents were really fine with the other party. The average Democrat gave the opposition party a 41, while the average Republican gave the opposition party a 38.

       Perhaps more importantly, there were very few Americans who had really cold feelings toward the other party. Just 10% of Democrats gave the Republican Party a zero in 2000, which was very close to the 8% of Democrats who gave the Republican Party a zero in 1978.

       Likewise, it was 7% of Republicans who assigned the Democratic Party a zero in 2000, compared with 5% who did so in 1978.

       The last two decades, however, have seen the opinion of the opposition plummet.

       The average Democrat gave the Republican Party a rating of just a 20 in 2020 -- a 21-degree decline in 20 years. This was even lower than the 26 that Democrats had given the Republican Party in 2016, an indication that the dislike of the opposition is still growing.

       The average Republican assigned the Democratic Party an even lower average score of 16 in 2020. This, like the score Democrats gave the Republicans, was the lowest score on record.

       Perhaps more amazingly, the percentages of Democrats and Republicans who flat out despise the other side are almost unfathomable amounts.

       Nearly a majority of Republicans (48%) gave the Democratic Party a zero on the 0-to-100 scale. This marks a nearly 600% increase in two decades. Slightly fewer Democrats (39%) give the opposition a 0, though this is a nearly 300% increase from 2000's 10%.

       But to be clear, it's not just that more Democrats strongly dislike Republicans or vice versa. Each party sees the other party as dangerous.

       According to a 2020 poll from the right-leaning American Enterprise Institute, 64% of Democrats see Republican policies as so misguided that they pose a serious threat to the country. Among Republicans, 75% believe Democratic Party policies are so misguided that they pose a serious threat to the country.

       When you see stats like that, it's no wonder that each party is at the other's throat. But in this climate, House Democrats are on record ( with just two Republicans joining them) in saying that portraying the murder of a colleague is beyond the pale.