Today’s Republican Party … is an insurgent outlier. It has become ideologically extreme; contemptuous of the inherited social and economic policy regime; scornful of compromise; unpersuaded by conventional understanding of facts, evidence, and science; and dismissive of the legitimacy of its political opposition, all but declaring war on the government. The Democratic Party, while no paragon of civic virtue, is more ideologically centered and diverse, protective of the government’s role as it developed over the course of the last century, open to incremental changes in policy fashioned through bargaining with the Republicans, and less disposed to or adept at take-no-prisoners conflict between the parties. This asymmetry between the parties, which journalists and scholars often brush aside or whitewash in a quest for “balance,” constitutes a huge obstacle to effective governance.

–Thomas Mann and Norm Ornstein

Mann and Ornstein are two scholars of American politics with a decades-long reputation for non-partisan analysis. This excerpt from their 2012 book, It's Even Worse Than It Looks, is quoted in Ezra Klein's Why We're Polarized where he talks about why Republicans seem unified in a way that Dems never seem able to be. Republicans can go deep, while Democrats must go wide. This requires that Democrats be more willing to compromise, which in turn requires that they be less ideological and fanatic. Klein writes–

The percentage of Americans calling themselves conservative has long dwarfed the percentage who identify as liberal. In 1994, conservatives outnumbered liberals 38–17. That gap has closed in recent years, but as of January 2019, conservatives still lead, 35–26. Three-quarters of Republicans identify as conservative, while only half of Democrats call themselves liberals—and for Democrats, that’s a historic high point. Self-identified moderates outnumbered liberals in the Democratic Party until 2008. What that means is Republicans have been able to appeal to their party through ideology. Democrats haven’t. They’ve had to appease a coalition of whites and nonwhites, liberals and moderates, the fixed and the fluid. They’ve done that by promising different policies to different groups—offering a transactionalist, more than ideological, approach to party building.

In their book Asymmetric Politics: Ideological Republicans and Group Interest Democrats, Matt Grossmann and David Hopkins offer the most careful study yet of the differences between the Republican and Democratic coalitions. What they find is that the Democratic Party is a diverse collection of interest groups held together by policy goals, while the Republican Party is built atop a more united base that finds commonality in more abstract, ideological commitments. (Why We're Polarized (2020), pp. 231-32)

So a couple of takeaways here.

First, Democrats are not nearly so ideological as Republicans. They are more practical and willing to compromise. There are ideological factions in the Democratic Party, but they do not dominate the party in the way that ideologues dominate the GOP.

Second, Republicans, notorious for their projecting their own attitudes onto others where they don't exist, see Democrats as they see themselves, as fanatics driven by ideology. They want to believe that the "squad" is calling all the shots. They're not. The Progressives coalition, for instance, lost the internecine Democratic fight about linking the vote for BBB to the Infrastructure bill. Democrats just want to solve problems. Ideologues and fanatics dominate in the GOP in a way that they just don't in the Democratic Party. The argument that both parties are equally driven by their extremists just isn't true. 

Third, Democrats are vulnerable to be identified with the ideolgues in their midst because in their diversity the Dems are a mashup of interests who too easily become identified with the sillier extremist, e.g., those who want to defund the police or who are caught up in some politically correct purity obsession of the moment. People who have these concerns, of course, have a right to fight for them, but the Democratic Party should not be identified with them at a time when democracy depends on the Party broadening its appeal.

Democrats are a mishmash in terms of policy substance, but Republicans perceive them as rabid ideologuues. But because no other identifying vision stands out in this mishmash, there's no robust, sane, positive counterweight to shape public perception. The extremist ideologues stand in the foreground crowding out the more accurate perception that most Democrats are moderate, down-to-earth problem solvers. The solution for this is for the Democrats to find what I've been calling a motivating Progressive vision that unites and inspires their broad representation of the American population–and perhaps might even inspire those independent thinking Republicans who are not ideologues. A vision that is Lincolnesque in its broader outlines to achieve a more perfect union, not so fragmented as to be identified with particular culture-war factions within the coalition. People should feel proud to identify as Democrats. How many do? I know I don't. 

A fourth point is that you can't run a democracy with one party unwilling to compromise, and that's why the future success of the Democratic Party is so important. Mann and Ornstein entitled their their book It's Even Worse Than It Looks because they saw in 2012, even with Romney as the GOP presidential candidate that year, that the party had already been captured by the crackpot ideologues that would inevitably embrace Trump. One of the worst things that MAGA world can say about a Republican today is that he's a Romney Republican. Those relatively sane Republicans have no place in the party anymore. Some have figured that out. Apparently Romney has not. I admire his integrity; I'm dismayed by his obtuseness. 

A fifth point is that the description that Mann and Ornstein give of the GOP above is a description that now fits the Supreme Court majority.