Now that they are relegated to minority political status in the District of Calamity, the progressive wing of the Democrat party feel free to impose purity tests and try to effectively take over the party.
One of the litmus tests for a Senate Democrat to show their loyalty towards liberalism is to oppose President Trump's choice for the Supreme Court, Judge Neil Gorsuch.
Senate Democrats may stew over a "stolen" SCOTUS pick, because the Senate Majority in the 114th Congress refused to hold hearings and scuttled former President Obama's lame duck Supreme Court pick Merrick Garland. This Senate Advice and Consent through inaction followed a 70 year precedent of not confirming SCOTUS picks in the last year of an Administration so as to let voters decide.
However some Democrats are so obstreperous that they will not meet with Judge Gorsuch, like Senate Minority Leader Chuck Schumer (D-NY). Those who consented to meet Judge Gorsuch have been charmed by him and his impeccable legal credentials.
Liberal advocacy groups like Credo Action felt emboldened by Schumer's antipathy approach thus they warned wavering Senate Democrats that if they so much even consented to a Cloture vote for Judge Gorsuch that they will face primary opposition in the 2018 cycle.
So Democrats opposed Republicans effectively filibustering Garland through a no vote yet they want to do the same thing to Judge Gorsuch. As Chris Plante is wont to say, if it wasn't for double standards, liberals would not have any at all. Ironically, filibustering will be futile thanks to the legacy of former Senate Majority Leader Harry Reid (D-NV) who invoked the nuclear option in 2013. Now all the current Majority Leader Mitch McConnell (R-KY) needs to do is expand the rule change in medias res to include Supreme Court nominations.
From an objective standpoint, Democrats threatening to primary vulnerable Senate Democrats to just allow a vote for a Supreme Court Associate Justice seems counter-intuitive. The Scalia replacement would not drastically change the balance of the court, so why come out with guns blazing against your own for a goal which is note a game changer.
Although Democrats only need to garner three net seats to regain control of the Senate, they face a tough election cycle in 2018 with 23 of 33 seats up. Incumbents have a much easier time fund raising and winning general elections, so why take out your own (even if they stray from the party line on some issues)? Furthermore, ten of the Senate races are Democrats in states that voted strongly for President Trump. Threatening to primary Democrat incumbents pushes them further to the left, which was not were the vox populi seems to be in those states.
If opposition from the left seems too strident, some incumbents like Senator Joe Manchin (D-WV) and Senator Heidi Heitkamp (D-ND) might conclude that the grass is greener on the other side of the aisle. Even if they do not politically defect, they may be emboldened to vote their conscience to keep their integrity or burnish their independence from a progressive purge to keep their seat.
It would seem prudent for progressives to not play hardball on this Supreme Court nomination but fight like hell if a senior liberal Associate Justice (like 83 year old Ruth Ginsburg or 78 year old Stephen Breyer) or majority maker 80 year old Anthony Kennedy decided to retire. But it seems that progressives do not want to leave any powder in reserve for such a contingency.
Even though objections to the Scalia replacement were packaged as being objections to Garland's no vote or automatically opposing President Trump's pick, it seems that progressives are concerned that reversing Roe v. Wade and throwing the adjudication of abortion back to the states is at stake.