In every democracy "all candidates are liars", if you call a liar anybody whose views can be contradicted by somebody else. Most of what candidates talk about aren't scientific facts, they are opinions and projections and moral judgements. Even about scientific facts there is considerable disagreement - what was considered a healthy diet a decade ago, is seen as a nutritional disaster now, so would a candidate that advocates old diet be called a liar? What about advocating current one - would such a candidate be a liar in a couple of years? Some economists think rent control and minimal wage are a disaster, others think they are a very reasonable and beneficial measures. If a politician agrees with some of them but not others - is she a liar? There's not a lot in what politicians say that can be scientifically and robustly verified as true or false - and those things that really can are largely inconsequential - even if some politician decides to proclaim pi equals 4, it's unlikely any actual policy would be influenced by that. So it would devolve into partisan bickering and gotcha hunting. Which you can amply witness on multitude of "factchecking" sites, which devolved very quickly from objective observers into presenting opinions as facts on one side into "factchecking" internet memes and obvious marked satire on the other.

That's a good thing. The views on governance policy can differ. I have no problem with those things.

I am talking about objective truths like Earth being flat, incorrect dates, misinformation in speech etc

There are grey areas here too, example being religion, and I concede that area becomes needlessly murky. Having said that, it needs to be discussed