Trump is the only candidate who is making a significant alternative foreign policy argument is Trump. It isn't an argument I agree with, but it is an argument. He insists he will be able to make better deals with the rest of the world than past presidents. He cities his business record as evidence. (This is questionable for many reasons.)
Overall the candidates agree that we need to defeat ISIS and just generally be stronger in the world. Sanders wants to do it with coalitions. Rubio, on the other side of the equation, talks about ground troops - although he actually has a more pragmatic understanding of foreign policy. But it is variations on a theme. The real outliers are probably Rand Paul (who's been demoted) and Lindsey Graham (who's dropped out).
There is also a sharp differences between the parties on immigration, but that - strictly speaking - is a domestic issue with big implications for other countries so I'll put it to the side.
The Art of the Dealmaker
Trump however is coming out against free trade. He insists that we are losing to the Chinese, the Mexicans, and the Japanese. Now yours truly believes in free trade. Big picture it helps everybody, but unfortunately capitalism involves a lot of creative destruction - which sounds good good in a lecture seminar, but in reality means lives being ruined. Most serious analyses find that changes in employment patterns are due to increased automation, not free trade. But trade has become a lightning rod for deep and legitimate grievances.
The United States has a long-standing commitment to free trade. Most countries have a Ministry of Commerce/Industry/Trade. We also have the United States Trade Representative devoted strictly to advancing free trade, while Commerce promotes U.S. products worldwide. Other nations find this confusing.
On the whole, free is good for the U.S. economy. By stimulating other nations economically it creates markets for more sophisticated goods of which the U.S. is a leading producer. If the U.S. imports sugar from Central America or textiles from Pakistan, U.S. farmers and textile manufacturers lose out, but those countries become wealthier and can buy smartphones, cars, software, and financial services. NAFTA was a component in the huge U.S. economic boom of the 1990s.
Trade also serves U.S security goals. The TPP, besides economic benefits, it strengthens security bonds and creates common communities of interest.
Long and short, as a builder Trump wants to maximize his work at the expense of everyone else in NYC. But the President of the US is not a CEO, he's more akin to the mayor, maintaining the system of order. In the short run the US might win some, but fundamentally the US maintains a system of global order - protects and even creates global commons. If we initiate a grab for more we will also set in motion a global tragedy of the commons, to the detriment of all.
Tactics vs. Strategy
But this post isn't really about Trump. It is about presidential efficacy. All of the candidates insist that they will basically be better at being president than Obama is or Hillary will be. Hillary of course insists she has more experience than anyone and knows how to be president.
And let's be clear, every issue is a negotiation, a deal. When the US acts militarily, it affects other countries. When the US delivers aid, it affects other countries. Even if we do not discuss our actions with them, well that is a "negotiation" tactic.
We like the idea of the President going mano y mano with Putin or whoever at the negotiating table and "winning." So many candidates insist that they know how to do this kind of thing. That is certainly one part of the presidency. It is tough to know if someone will be good in this situation or not. My inclination is that anyone credibly running for president probably has what Schumpeter called "force of personality."
Besides that, just being president is a pretty significant power plus up! And of course a president has limited time and energy. They can get personally involved in an issue, but they will need to pick that issue carefully out of the literally hundreds that need to be addressed.
So consider Nixon, probably one of the least personally impressive presidents. He didn't like confrontation and was introverted. He found campaigning and gladhanding painful and was consistently awkward at it. Yet he was very effective. That doesn't mean I like his decisions, but rather that if he wanted to achieve a policy goal he was pretty good at getting it done.
Each deal, incredibly complicated in its own right, needs to be more broadly considered in two dimensions, time and space. How how will a deal we make with China today affect our relationship with China in two years or five years or twenty years. Because China will continue to be a factor. If we browbeat them into concessions now, will that hurt us farther down the line when we need something else from them. Also, whatever we do with China affects lots of other players. How will a particular agreement with China affect our relationship with Japan or India. Further, those relationships move in time as well. So how does negotiation today with China shape our relationship with Japan in five years? But wait, there's more because major international issues have a domestic component (Putnam's famous two-level game.) So every negotiation is a complex operation in its own right that also shapes and affects a huge range of other issues.
So which more valuable, a brilliant tactical negotiator or a brilliant strategist who chooses where and how to apply resources - including their own time and energy. Ideally you'd have both. Most people who reach the presidency are pretty capable. But strategy is another story. It would be nice to have a president who can win battles, but better one who can win the war - that is consider the panoply of U.S. interests and advance them broadly.
Estimating Presidential Efficacy
So how do we judge whether someone is up to high office. There is the resume/experience analysis. We can't know beforehand how capable someone will be. But, we can get at least a sense of their familiarity with the issues. Complex foreign policy issues have a pretty steep learning curve. Familiarity beforehand is an advantage.
On that one, Hillary wins hands-down (she of course has other negatives). 8 years as First Lady where she got a good look at what is involved with being president. Organizing ones time and staff are underestimated but significant challenges. She spend 8 years in the Senate and was well-regarded, then 4 years as Secretary of State. So she is familiar with the national security bureaucracy and the legislature and handled a variety of issues.
Kasich would probably be in second place. He spent 18 years in Congress, all of them on the Armed Services Committee. He was also governor of Ohio for 5 years. I happen to think gubernatorial experience is over-rated as preparation for the presidency, but I wouldn't argue it was irrelevant.
After that, probably Bernie Sanders, who has served on Capitol Hill for 15 years. Granted, he has shown little interest in foreign policy - but at least those issues crossed his desk. He is also familiar with the ways of congress.
After that it gets thin. Rubio and Cruz have first-term Senators with few accomplishments to their name (although there is some modest evidence that Rubio has at least thought seriously about foreign policy). Favorite son Martin O'Malley, Christie and Bush were/are governors - which represents significant political experience, but not real foreign policy experience.
Carson and Trump have no relevant experience with the nuts and bolts of foreign policy.
I'm ready to believe most of them are pretty capable negotiators. But have any of them shown a real capability to think strategically across the huge range of issues facing the United States in a world in flux? Can any of them "keep the whole equation in their heads?"