Most of the liberal agenda isn't popular enough to push legislatively and hasn't been for a very long time. Many of its biggest successes has been achieved using legislative end-arounds via the courts and judicial activism, or executive fiat. On its own merits it tends to die on the vine using the standard method of passing bills into law. As an example, how many times did we see gay marriage ballot initiatives get slaughtered at the polls in state elections around the country, and ultimately succeed by circumventing the legislature?

The republicans denying confirmation of Obama nomination Merrick Garland to replace the reliably conservative Justice Scalia made the 2016 presidential election a must win at all costs imperative for the liberal agenda in America because the courts were literally last vestige of hope for its future. After the Gorsuch confirmation it was scorched earth politics for the left from there. That's why the Kavanaugh confirmation was the shit show blood fest that it was. If Trump gets another pick we may just have a civil war on our hands. The liberal ideology in America is staring an existential threat in the face and the demagogues are getting desperate.

Should restrict the ability to add justices. I can't see a reason why we should need more than 9. Make this an amendment as part of the Convention of States.

[conventionofstates.com]

That’s the only way the democrats could get their radical left wing agenda.

Democrats aren't in position to pack the court.

There needs to be a term limit set. Some of these people are so old and have been in since Moses walked the earth.

It is indeed a dangerous tactic. Mostly what I'm surprised by is how many democratic candidates have tipped their hand by admitting that they consider this a valid strategy. I'm surprised such statements aren't followed by, "Oops! Did I say that out loud?"
So... if the next democratic administration adds enough seats to gain a liberal majority on the court, and then the next conservative administration adds enough seats to tip the balance of partisan power his way... I believe that describes an equation of geometric progression.
That's a whole lotta robes.

Mostly I think (and hope) that the net effect of dem candidates admitting that they would even consider such a thing is to guarantee a strong republican turnout in the next election.

Marxist criminals packing the court is disastrous