True. I see that Parliament also has a Speaker of the House with a similar role to the US Speaker of the House. I was confused why you equated the Prime Minister with the House Majority Leader, rather than the Speaker of the House. It sounds like in the UK, when a party gets a majority in Commons, their leader usually becomes PM, while in the US, their leader becomes Speaker.

The President in the USA can veto laws. In a Constitutional sense, this gives them more power than any other single legislator. They are also the leader of their party, which can make them just as influential as the Speaker of the House (House Majority leader) when their party has the majority. The public also pays more attention to the President than the Speaker. For these reasons, and because Presidents have defined terms, it’s convenient shorthand to describe a period of time.

The ‘selective enforcement’ occurred because strict enforcement would be much more expensive than what anyone wanted – yet a fanatical minority was able to play games in Congress to repeatedly block bipartisan deals for “comprehensive immigration reform” (under Bush, Obama, and Biden).