The magnitude of the shift was certainly not matched by a magnitude of serious deliberation.
Democrats decried the hypocrisy of the Republicans who had refused to hold a hearing during an election year when President Obama nominated Judge Merrick Garland. The Democrats also sounded alarms about the likely ramifications of an ideologically conservative Barrett replacing liberal Ginsburg. Republicans, not surprisingly, insisted that there was no such hypocrisy. They also lauded Barrett's avowed judicial restraint in decision-making, while insisting that her asserted embrace of originalism and textualism had nothing to do with any perceived ideological bent. After four days, the pre-ordained result seemed nothing but pre-ordained.
Whatever the partisan wrangling and dissembling may otherwise suggest--about the Barrett nomination and Barrett herself--there are some simple realities. Ruth Bader Ginsburg was selected by Democratic President Bill Clinton. She was heralded for her successful litigation on behalf of equal rights for women, and her record on the Court over 27 years was unmistakably liberal across the wide swath of issues from abortion rights to affirmative action to gender equality to immigration to LGBTQ rights to racial justice to the rights of the accused, etc.
By contrast, Amy Coney Barrett was selected by Republican Donald Trump. Her nomination was urged by supporters because of her ideological leanings that are distinctly contrary to those of Ginsburg, and for her judicial record which, albeit brief, reflects a polar opposite jurisprudence. In short, by all accounts, she is very ideologically conservative.
So let's take a look at the change that's in store--a change for the Court with a Justice Barrett who presumably would behave consistently with her record as Judge Barrett.
Here's what the ideological line-up of the Justices looked like in the immediately past term, with Ginsburg still on the Court:
(click to enlarge)
Based upon the politically conservative groups that urged the nomination of Judge Amy Coney Barrett, the promises President Trump has made about the kind of judges and Justices he would nominate, the support Barrett has been receiving from politically conservative Republican Senators, her academic writings and lectures, her record as a federal appellate judge--based on all of that evidence, there is every reason to believe that a Justice Barrett would be positioned firmly within the politically conservative wing of the Court. That is, there is every reason to believe that she would be voting with the politically conservative Justices on the politically conservative side of the liberal versus conservative, "hot button" issues.
Based on the previously listed evidence, it is safe to assume that her ideological bent is no less conservative than that of Trump's first two nominees, Gorsuch and Kavanaugh. Indeed, she might well be even more ideologically aligned with most conservative among the conservative Justices--i.e., Thomas and Alito.
At the least, her appointment to the Court would alter the previous 5 to 4 politically conservative majority on the Court--or the arguable 4 to 4 ideological balance with Chief Justice Roberts as the "'swing" vote. That would change to a 6 to 3 conservative majority--or arguably a 5-4 conservative majority with Roberts splitting his votes between the Court's two ideological wings. Putting the change more starkly, Judge Barrett's addition to the Court, filling the Ginsburg vacancy, would mean twice as many politically conservative Justices on the Court as liberals. Even more stark? The politically conservative Justices would still constitute a majority without Roberts' vote. The liberals on the Court would need two of the politically conservative Justices to vote their way to ever reach a majority.
To be sure, it is within the realm of possibility that Judge Barrett might experience an ideological and jurisprudential conversion over her tenure on the Court. It has certainly happened to others. Republican appointees have sometimes transitioned to staunch jurisprudential liberals. Nixon appointee Harry Blackmun, Ford appointee John Paul Stevens, and Bush (41) appointee David Souter come readily to mind. And Reagan appointees Sandra Day O'Connor and Anthony Kennedy, even if never quite liberals, both became "swing votes" during their tenures, joining their liberal colleagues on some major social issues.
Absent such a dramatic ideological transformation, however, Judge Barrett's addition to the Court will result in a dramatic ideological transformation of the Court itself. Amy Coney Barrett replacing Ruth Bader Ginsburg? That is dramatic.
One more note before concluding. Imagine for a moment that remote chance that the Barrett nomination were to fail. What would the Court look like if a President Biden, rather than President Trump, were to fill the Ginsburg vacancy? Take a look:
(click to enlarge)