Originally Posted by yellow77

The terms of the alliance with UA do not allow CO to sell a codeshare on UA for a domestic nonstop segment like this, if bought by itself. It is not surprising you can't buy a CO-coded flight on DCA-ORD stand-alone, because it would be illegal for CO to sell it. It was structured this way so as to pass antitrust considerations with the DOJ and DOT.

The only possibly stupid thing would be for anyone to buy what CO offers here. It's not stupid for them to try to sell it. If you want the UA nonstop, don't try to use co.com as your travel agent.

The OP never said he was flying only CHI-WAS; he is presumably connecting from somewhere else (again, possibly on a CO code: there seems to be no issue with CO selling connecting flights on UA under the CO code).