Writes the WaPo fact-checker Glenn Kessler.
I got there via "WaPo Fact Checker Glenn Kessler Morphs Into WHO Apologist in Ridiculous Fact Check on Trump" by Sister Toldjah (at Red State), which is near the top of my favorite source for new news links, Memeorandum.
IN THE COMMENTS: That "Trump really gets over his skis" prompted Danno to write:
Kessler a ski jumper? Laughable. But maybe someone should strap some skis on Kessler and release him from the largest ski jump in existence. Now that would be fun to watch.Is "over his skis" a reference to ski jumping? I looked it up and fell right into the most famous "out over his skis" in history — spoken by Barack Obama and about — of all people — Joe Biden:
A few weeks ago, when Barack Obama was called upon to explain whether Joe Biden was officially authorized to endorse gay marriage, the president explained, “He probably got out a little bit over his skis, but out of generosity and spirit.”...Hmm. Interesting. But I still don't know if "out over his skis" refers to ski jumping or ordinary downhill skiing. I'm guessing it's the latter — simply because the ski jumpers I've seen on TV do this...
[T]he phrase’s metaphorical use seems to have begun in the finance world. Its first non-skiing print usages came in the early nineties, in publications like Investment Dealers’ Digest. For instance, a 1991 article quoted a “market source” describing a race between Goldman Sachs’ and Lehman Bros.’ preferred stock desk. “Someone said [Lehman] couldn’t get a clean legal opinion on it. They may have been out over their skis a little bit with their structure.”...
[W]herever Obama picked it up, it’s a way of taking someone down a peg without being too terribly harsh. Who ever thought a rousing defense of the right for gay couples to marry would be couched in such a bro-ish metaphor?

... which is to say that getting "out over your skis" seems to be what you're supposed to do. Kessler left out the "out," by the way, so I think he was out over his skis in the use of trite slang.
Anyway — to extend the metaphor — maybe if the skier looks out over his skis it's because his sport is ski jumping and you're thinking of downhill. That needs some work, but I offer it as an alternative to the usual "Trump is paying 4D chess."