Well, that's what happens when you have a president signing such agreements without getting them passed through the US Senate. You had an agreement with Obama, not America. Hopefully you have learned your lesson.
But would the US be happy if it entered into a deal with another country and that country backed out when it elected a new leader? That could happen with Mexico and the NAFTA negotiation, Mexico will have an election in a year and they may elect a really left wing Anti Trump President, the current President is very unpopular and anti Trump feelings are high in Mexico.
The problem is Trump does not present himself as a fair deal maker, he presents himself as someone will actively screw over the other side. Maybe that's bluster, but that attitude does not promote trust.
Trump has said trade with Germany and Canada is unfair, but it seems like he takes one or two trade disagreements and blows up it to say the entire trading relationship is like that. He only sees the negatives, never the positives and always presents America as a victim in these trade deals (its not) and really no nation would want to go out of their way to be helpful towards a leader with such a selfish attitude. He seems less about trying to strike a balances between two countries' interests and making an actual fair deal, and more making a deal where the US wins and the other country loses.
What kind of trade deal does he want? One where the other side has open its markets completely and Trump gets to put protectionist measures on the US market at a whim? No rational country would agree to such thing.
Are there legitimate trade gripes the US could have with countries, sure, no trade agreement, but don't assume the opposite is not true and these countries don't have legitimate gripes with the US. Just saying the US always plays fair and these other countries always cheat, is a rather naive, a lot of countries try to press an advantage during negotiations, but ultimately you have come up with agreement that works for both sides, just saying the US should win and the other side should lose, is a good way to start a trade war.
A trade war would hurt American workers, not help them:
https://www.nytimes.com/2017/05/31/us/south-carolina-bmw-us-german-trade.html?_r=0
https://www.theatlantic.com/business/archive/2016/12/mexico-nafta-trade/510008/
This is exactly how many American jobs depend on Canada?U.S. trade
And just to be fair, I think Trump can point some bad practices its partners make and ask that they be corrected like this:
Donald Trump, of all people, may prove to be the best friend of the Canadian consumer: Neil Macdonald - CBC News | Opinion
So I am willing to concede that Trump can be right about some trade practices simply not working.
Now this whole point about trade I am making feeds back into a greater point about Trump and the US' allies, that the US' allies do not trust Trump to be an honest broker on anything, whether its NATO, trade, environmental agreements, etc.
Just saying "the US saved your butts in WWII'' doesn't make Trump more trust worthy. Trump can make these deals easier by being a little more trust worthy and reasonable, if he doesn't, if he seems to prefer fantasies to facts and play everything like its a zero sum game, he is going to make negotiations on a lot of this stuff harder and that could lead to stuff like trade wars and that will harm the American worker.