The phrase is actually 'toe' the line. It comes from a sailing tradition, back when the crew was made to form into ranks, there were lines drawn upon the deck, and each was made to put their toe upon it.
Additional context is the idea that to go past the line, to do more than put a toe upon it, would be to invite consequences.
Trump is not a politician he is a patriot first and businessman second.
True but he's technically a politician now that he's president.
He's not acting like a politician, that's why they hate him, he's not towing the line.
The phrase is actually 'toe' the line. It comes from a sailing tradition, back when the crew was made to form into ranks, there were lines drawn upon the deck, and each was made to put their toe upon it.
Additional context is the idea that to go past the line, to do more than put a toe upon it, would be to invite consequences.