You have to wonder how can America needles so many countries--Russia, China, Iran, Pakistan--and even Turkey--and not expect to lose some leverage? Didn't Obama create an 'opening' with Iran, against great domestic opposition and political risk, especially against The Lobby? That was diplomacy!
What we have now? Some people give too much credit to the American political class decision making: "They think decades in advance..blah blah". They often do. But a POTUS holds a lot of power to make adhoc decisions. There have been major deviances in policies Trump has made vs what Hillary might have made. Examples like recognizing Jerusalem, getting out of the Pacific trade agreement, getting out of the Paris Accord, trying to needle Iran again, drilling in protected lands, tax reforms for the rich, with consequences in the future, trying to get rid of Obamacare... They are major decisions with long term consequences and they are NOT well thought out.
Trump is a threat to Americans and America's interests.