1) How does he understand foreign relations? Just building businesses abroad doesn't mean you understand diplomacy. He's short tempered, puerile, and loves to pick fights. He'll destroy foreign relations. Half of Europe already hates him. The UK tried to stupidly ban him. And he has no sense of subtlety.
One strategy that Trump has used during his campaign is that if someone hits him, he hits back harder. So far that has been very effective and only poor Jeb still consistently attacks him, in vain. That works just as well in international politics as in GOP primaries.
Trump is not short-tempered. He can be inflammatory if he chooses to, and he deliberately picks fights with his opponents, with those fights almost always ending in his victory and their defeat. He doesn't pick fights he knows he'll lose.
Most of Europe hates the GOP and thinks that Obama is a jesus. The Nobel committee gave Obama the Peace Prize for being black. Just goes to show that the European media and establishment is extremely biased. Half of Europe hates Trump? So what.
2) "Common-Sense Policies" - besides his deportation and border defense proposals I can't name another "common-sense" policy of his.
I'd be surprised if he actually built a wall or deported all illegals. He just says that to get into the headlines, but he will actually be a lot more moderate. I don't care if he builds a wall or just strengthens border forces, as long as he deals with the issue.
3) "Man of Reason" - LOL. Yes the man who's changed party, ideology, and policy positions more times than I can count is a man of reason. You're being duped in my opinion. This guy stands for nothing and believes in nothing other than what will get him elected. He's using the GOP base and we're all in store for either a huge betrayal if he wins or a catastrophic defeat if he loses, because if he loses we'll also lose the Senate, several Governorships, and the supreme court.
Just goes to show that he's neither a hardcore Republican or Democrat but an Independent who acts based on issues and not dogmatically by ideology.
Trump is someone who gets things done and has a lot of support across party lines. He doesn't have to sign executive orders to get his way, like Obama and probably Cruz who has recently alienated the GOP establishment. A lot of people don't agree with Trump but they can still work with him.
Republicans *need* to get rid of some guys who are still living in the 1980s, and replace them with better candidates. They might lose a few governorships, but they will gain a lot of new ones.