The Democrats are refusing to comment on it to cover their bases. If they win, 'We didn't say we wouldn't do it, and we need to so we can save democracy!'. If they lose 'We never said we'd do that, and if the Republicans do it they're attacking democracy!' A definitive statement can't help them and will definitely hurt them, because they absolutely plan to pack the court but saying so will hurt them now and lying about it will hurt them later.
If you're not willing to abandon a party when they abandon you, you're not a voter; you're a serf.