`No`, responded MacDonald, `But I do know a little about politics

Spot on.  This not about Mulroney's serenading Trump's pals, it's about politics.   Sir John A MacDonald was a crafty political animal, disliked by many but he promised the railway as bulwark against American expansion. The debate in the Commons was bitter, often spiteful.  He was pilloried in the press but his political gamesmanship got us the railway.  

There is something peculiarly diseased in the minds of people who would unilaterally hate a politician.  Bill Clinton was a womanizing and manipulative philanderer but many would argue the USA and the world did well under his rule.   That's politics.