I don't think isolationism works, either.
Is that the same thing as "America first", though? Because I do agree that our first obligation needs to be to the United States.
Also, I think that it's possible to have allies, without supporting them in every endeavor. We should have mutual defense agreements, but should we pay more than our share? Isn't it fair to require contributions from our allies? And, when nations openly defy us at the United Nations, is it fair for there to be consequences? Is it our job to subsidize the countries that spend their budgets in ways that harm the United States?
Partnerships and allegiances need to go both ways; it can't always be the United States footing the bill and supplying the troops, while other countries openly defy and criticize us.
Keep in mind, too, that Mattis is advocating an aggressive foreign policy that has us engaged -- with boots on the ground -- around the world. Mattis is very much a part of the Military Industrial Complex who is fairly interventionist. His is a foreign policy that supports interventions in Iraq, Syria, Libya and a whole host of other quagmires. I'm sure he would have been big on the Vietnam War, as well. As I get older, I become less and less in favor of having our sons and daughters killed for no reason other than geopolitics.