@rightminded, here goes a FEW examples:
1. He revealed highly classified secrets to the Russians in the Oval Office without telling our allies and put our source at major risk. (https://www.businessinsider.com/trump-revealed-highly-classified-information-to-the-russians-2017-5)
2. Trump has repeatedly trusted Kim Jong Il, a dictator with nuclear weapons, and when proven to have been fooled over Kim’s supposed halt to nuclear weapons development, lifted sanctions anyway, and ended military exercises with our ally South Korea – which makes South Korea directly vulnerable
3. He has repeatedly bent over backwards to help Russian oligarchs – AKA “mob bosses,” given the politics there
4. He has alienated our REAL allies in Europe by his misstatements over NATO, he has alienated the UK (happens when you lie about the Royal Family investing in Mar-a-Lago), he has threatened tariffs on many European goods
5. Let’s not forget we do a substantial amount of business with Canada and Mexico, who were allies until Trump launched trade wars and insisted on his nonsensical overpriced wall
6. He has undertaken a “decapitation” of the leadership of Homeland Security, evidently because he wants to put in his own people or is paranoid about them, but this puts our entire nation at MAJOR risk, given that there is almost no continuity of knowledge. He has set them back YEARS.
7. He not only failed to fill staff at the State Department, which is on the front line to track and negotiate with our enemies AND allies, but he wanted to cut their staff by 25%. This puts us at a major disadvantage against other nations like China and Russia, who have been positioning themselves as better partners (https://www.vox.com/policy-and-politics/2018/2/12/17004372/trump-budget-state-department-defense-cuts)
8. While we’re at it, we have lost influence in Asia, the rapidly-growing part of the world, because on his FIRST DAY, Trump withdrew from an Asia pact. Guess who benefits?