I'm not a Republican, but I'll bite.
The U.S. is kinda in a bad spot right now. Not just politically but economically as well. Our National Debt is the highest it's ever been. While I'm 100% for taxing Billionaires and their Trillion dollars companies more, by like, a lot, the Billionaires of course don't want that. So they're trying to cut what they can and wheel and deal. Why support Climate Change (French EU thing, I don't remember) acts when you can [pocket the money] use that to pay down debt? The War in Ukraine has unfortunately been drawn out too long for us to stay financially invested in it. Our allies across the sea won't be able to help our country balance our debt when they have Ukraine to worry about as well. So they've decided to put pressure on every external source of revenue while cutting what they can without getting lynched.
Let's talk about Canada and Mexico, but first, a bit of H I S T O R Y. Back in the 90s or 00s the Clinton Administration implemented NAFTA. The agreement sounded good on paper: Strength our border countries. Lifts us all up by giving all the countries jobs, more opportunity, more demand. While outsourcing our manual labor we can focus on the future: Technology! Hindsight is 20/20 though. Why not move our business to a country where we pay lower wages and will end up with higher profits for future investments (like yachts)? Why not get cheaper parts instead of paying the U.S. prices? A ton of manual labor jobs were lost, and many cities (car manufacturing cities, steel cities, etc.) simply never recovered. NAFTA stayed in place more or less until Trump Trumped it into the USMCA in 2020. That gets renegotiated in 2026 with all 3 countries either coming to an agreement or dissolving the agreement.
From all accounts, NAFTA certainly seemed harmful to the American industry at the time, but can that industry recover, and should it? Personally, I don't think so, but they seem to think so. So, from my point of view, the reason they're alienating allies is to extort them for money to help pay down the National Debt and hopefully grow back American industries lost over 2 decades ago.