I think it depends. So many relevant variables about when you draw a line.
eg Trump's Access Hollywood tapes (the "I don't even wait. And when you're a star, they let you do it. You can do anything. ... Grab 'em by the pussy. You can do anything."). He wasn't a politician, just a TV personality. Should we ignore it as "pre-politician stupidity" or should be consider it along with current behaviour?
I would call that illegal and harmful.
But yes, a pattern of behaviour cannot be ignored.
And leader of the free world, is slightly more high profile than Reform candidate in a by election. So probably deserves more scrutiny.
It's an interesting aspect and one very subject to personal bias.
I suspect that what Trūmp said was not illegal but were he to do what he said it would be (and he doesn't always seem to be 100% truthful). A confession or showing-off with lies?
But either way somebody's past can provide a helpful appreciation as to who they are now.
I can appreciate the aspect that liking what somebody else said several years back ... could be a bit OTT but consistent liking of many posts from others supporting a particular view can again help understand their underlying beliefs.
eg Faråge's behaviour at school, letters from his teachers, etc. relevant or to be dismissed? Trouble is much of the reported behavious sort of fits with the attitudes I see from him today so to me useful in that it suggests likely a deep seated pattern of attitudes unlikely to change eg on new information/statistics.
Hence a balance, it depends.