Does that mean shouting “You lie!” as one Republican did to Obama is OK, or does that cross the line? And say, what did other Republicans do to sanction him about that behavior? Inquiring minds, and all.

No, it does not. But that's the point. The Democrats spent a lot of political capital distinguishing themselves from the GOP as defending the "guardrails" of democracy - the 'rules' of government that haven't been formally codified.

Generally, if you want voters to choose you because you're different than the other party on a given point, then you can't do the same things as the other party on that point. If you do the same things, then it undermines your argument to voters that the opposing party's failure to comply with those norms represents an atrocious breach.

That same dynamic explains some of the Democrats' reticence to use the debt limit as leverage to force changes in, say, how DOGE is taking a wrecking ball to the civil service. The Democrats spent a lot of time characterizing anything other than a "clean" debt limit raise as metaphorically holding the country's fiscal health hostage, an illegitimate tactic in order to let the minority dictate policy to the majority. The GOP tried anyway a few times, which the Democrats can point to as justification for pursuing that tactic themselves. But if you do that, it undercuts a bit of your argument that the GOP was doing something really wrong when they were doing it, and you end up tacitly supporting their then-claim that doing so was legitimate politics and not something egregiously wrong.