LO$\mathrm{.}5$ Casey is a U$.$S$.$ citizen employed by a multinational corporation at its London office. Casey is married to Michael, a British citizen, and they reside in England. Michael receives substantial rent income from real estate he owns in western Europe.

Must Casey file a U$.$S$.$ income tax return?

Under what circumstances might Michael be considered a resident of the United States? Would such a classification be advantageous? Disadvantageous? Explain.