Girlboss Sinema has likely ruined her political career

No, this is literally the fallacy of centrism and American moderate delusion. Because normal people can't possibly believe the GOP really is this bad they think basic facts about reality are just actually partisan.

You see something similar when it comes to Republican voters and policy:

https://dataforprogress.org/blog/2020/12/30/republicans-dont-know-anything-about-their-party

The political scientist E. E. Schattschneider argued that “democracy is unthinkable save in terms of the parties.” For Schattschneider, parties solved an information problem that arises with advanced (post-)industrial society. Put simply, the kinds and quantity of policies that arise are of such complexity and scale that no one person could ever hope to know enough to make an informed voting decision. The parties then are to work as heuristics. With their platforms they work to simplify the great issues of the day. But if this metric by which we are to judge their relative success, they have evidently failed.

In 1950, a committee Schattschneider chaired released a report called “Towards a More Responsible Two-Party System.” The report advocated for, in brief, more ideologically distinct parties which would offer voters a clear choice. Recent trends in partisan polarization have caused voters to question this conclusion. But these findings suggest that despite the ideological drift of the parties in Congress, voters don’t always see the choices they have as being distinct on issues where the parties are in fact quite different.

As for why Republicans voters in particular don't see a difference between the two major parties, there are many causes. Motivated reasoning likely plays a large role. If a Republican voter doesn’t think mining companies should dump debris into a stream, why would they think their elected representative would support this policy?

This is a long-running trend, of voters, especially Republican voters, denying the extremism of the positions that the party holds on questions of political economy. Matthew Yglesias, formerly of Vox, terms this phenomenon “the politics of incredulity.” For him, such voters are a major reason why these conditions persist. He argues “voters find [the Republican Party’s position on economic issues] so outlandishly bad that they’ll only believe someone espouses them if you can convince them first that the person in question is a heartless monster.” For Republican voters in particular, Yglesias adds: “Consequently, people who align with Republicans on broad values themes — whether opposition to abortion rights, love of guns, patriotism, or panic at the thought of a diversifying country — find it simply not credible that their champions are actually running on a politically toxic agenda that would clearly lose elections.”