We're not talking about the philosophical elements of politics for the most part. There are plenty of parts of government policy where there is an objective truth and one side (or even both on occasion) are trying to manipulate the narrative away from that.
To use a non-US example: Boris Johnson claiming that he is going to deliver 50000 more nurses in the NHS. Except that figure includes some 19k nurses who are already employed in the NHS.
Back to Trump: Great, but we also won the election!
Donald Trump objectively did not have the largest inaugural attendance of any president. Windmills objectively do not cause cancer. It's objectively true that we should not nuke hurricanes. You could fill pages and pages of examples of objectively false statements, not just things the left and right disagree on.
Yes, but the objectively false statements that the left and right don't disagree on are not politics.
Politics is pretty much what's left that we disagree on, that can't be settled objectively in other domains. And is an expression of people's values, like what's the right way to live a good life, is there even more than one, who's gonna get the rare exclusive things in life that we can't all get (e.g. apartments with views on Central Park or your local equivalent).
There's enough variation in these values that we can't agree on these things and they conflict. Hence, politics.
Whatever you want to call it, it's clear that the left and right disagree about actual objective facts, not merely goals or their policy agenda, and that these disagreements drive (and are driven by — the causality can run in multiple directions) political support and decision-making. Right now there's a big debate about whether there was widespread fraud in our recent election (though I would be remiss not to point out that there doesn't seem to be any credible evidence for that). That's a politicized factual dispute, the adjudication of which (by which I don't merely mean in courts or the Electoral College or what-have-you, but also in the public's perception) will have fairly profound real-world consequences for some years to come.
That is one of many recent examples of these sorts of politicized factual disputes.
What is objective truth in politics ? It's the most non-objective aspect of society there is, arguably even more non-objective than art.