Is the call of the President of the United States a liar? As Kellyanne Conway proposed on CNN?

It depends on whether it is true that Trump tells lies. When Trump was first elected, NPR went into detail on what exactly a "lie" is. Making a false statement can be a lie or not. A lie is when a person purposely makes a false statement in order to deceive someone in order to obtain a secondary gain. That's a lie. But if someone spits out false information without knowing that it is wrong or doing so for a secondary gain, that is not a lie. It's just wrong information instead.
For example, if Obama said that he would carry out his campaign in all 57 states, that is a false statement, but it is not a lie because Obama is misinformed about how many states the US actually has.