I think we just gotta ask ourselves... If a president will lie about something as trivial as his weight and height... What else is he gonna lie about? How can we trust him?
You’re right.
But the issue is Trump lies endlessly. One side know this and are bemused that he has ended up in power anyway. The other side just don’t care about his endless lies or have somehow deluded themselves in to believing he doesn’t lie. From the other side of the pond it is all a bit baffling. But we had similar with Johnson over here.
The problem here is the poor quality of arguments. Recall this argument you made about Boris Johnson, proudly announcing your "favourite" lie of his. It was poorly researched:
My "favourite" (if that's the right word) Boris example was when he went to a hospital for a photo-op and was accosted by a parent of a patient there. The man lambasted Boris about the lack of resources and for coming to the hospital for a photo-op. Boris denied it and said something along the lines of "there are no press here" in front of the press who were recording the encounter. 
Your "favourite" example is actually an embarrassing display of your tendency to assume things which suit you without considering that you might be wrong and that you need to research your positions. Obviously "there are no press here" can mean a lot of things. Namely that they weren't acting as press. It's not too hard to find that this was the case:
https://www.channel4.com/news/factcheck/factcheck-qa-what-did-boris-johnson-mean-when-he-said-there-were-no-press-at-his-hospital-visit
Omar Salem was waiting for his daughter to be treated in a paediatric ward in Whipps Cross hospital in northeast London when he confronted the Prime Minister, saying: “The NHS is being destroyed… it’s being destroyed and now you come here for a press opportunity.”
Mr Johnson replied: “Well actually, there’s no press here.”
Gesticulating at the members of the media standing nearby, Mr Salem said: “What do you mean, there’s no press here? Who are these people?”
Mr Johnson appeared to start an attempted explanation, saying: “They’re… they’re here…” before trailing off.
Who was at the event?
Downing Street invited a photographer and a video crew from the Press Association – the UK’s news agency of record – to the event, as well as a “pool” video crew, consisting of a camera operator and broadcast journalist.
The long-established pool system involves the major broadcasters (including ITN, the makers of Channel 4 News) taking it in turns to send cameras and journalists to events that we know about in advance.
Footage shot by the pool camera crew is then made available to other members of the pool for use in their own broadcasts.
Often, the pool team agrees to go to the event on the understanding that a reporter will get the chance to ask questions of politicians like Boris Johnson.
Obviously, if only one reporter attends, that limits the scope of the questions, but the questions aren’t pre-arranged with the government and there’s no restriction on what journalists can ask.
On this occasion, the broadcasters who run the pool were told that they would be able to film Mr Johnson walking around the hospital visit, but no arrangements were made to record an interview the Prime Minister, or ask him questions.
The pool team agreed to go on this understanding. Apart from the Press Association, it appears that no other reporters from newspapers or other news organisations attended.
This may have been what Mr Johnson had in mind when he said there were “no press” at the event.
It wasn't a press event. You were assuming too much. A person who is taking photographs or video in a hospital to document a state visit isn't necessarily acting as "press". The relative of the patient was questioning Johnson about the absurdity of the presence of press at the hospital, but Johnson pointed out that consideration was given. They were not acting as press by agreement.
Johnson's use of "actually" in his response of “Well actually, there’s no press here" suggests that they may seem like press, but are not. This should have prompted additional research on the actual situation rather than just assuming things. Johnson is suggesting that he knows something that the relative didn't know, which an astute investigator should have looked into before embarrassing themselves with false and faulty partisan accusations.
These "lies" seem to hinge on your own intelligence and ability to research and comprehend truth, which puts your assessments into serious question. Considering that you apparently believe every liberal trash article you come across, we can safely dismiss your disreputable claptrap.