Well, please understand that I'm being a bit mischievous here. I realize that the Senate had no intentions, anyway, of saying that presidents can lie under oath without fear of substantive repercussion.
But that was the folly of their action. It really doesn't matter what they did or didn't intend. Because it was plainly obvious to everybody that he did lie under oath -- even to the point where he accepted a settlement that included, among other things, his disbarment -- their acquittal, whether they intended to or not, did actually establish a problematic precedent.
My point here has nothing to do with Trump. It's really more of a slam at the Senate -- they shouldn't have done what they did there. I understand why they didn't want to. And I'm sure a lot of the Senators at least gave a cursory consideration to what their acquittal would mean going forward. But, ultimately, the vote once again just fell down (pretty close, anyway) along partisan lines.
And I think in that they -- unintentionally, I'm sure -- caused some harm to the country that wasn't evident then, and might not even be yet. The message from that episode is clear enough -- so long as a president maintains enough friends in Congress who value his agenda more than their duty to faithfully uphold the Constitution and their duty as proscribed by it, he probably has nothing to worry about....at least to a further extent than existed prior to 1998.
I'm not cheering this, BTW. I'm scolding the Senate for having done it...even if they didn't intend to.