The problem is that Air Azul goes to BWI only. I've made the MARC run from BWI-Union Station more times than I care to think, but it's still a time consuming process, especially if the weather is crummy.

You can usually count on LAN-DTW-DCA flights around $200. For my money, I'd rather have a connection in DTW, which is usually only around an hour, than fly nonstop to BWI and have to deal with at least three modes of ground transportation to get into the district.