Why not move the azalea? It's unusual to cut down a tree to save a shrub.

I don't think you should do anything until you determine the problem. Azaleas like really acidic soil. They also have a shallow root system so they are going to have trouble in soil that is shallow and not very fertile. If the tree is a rather aggressive species, the tree roots may be outcompeting the azalea roots. If the tree has a rather thick canopy, it may be too dry underneath the tree for the azalea to thrive.

Thanks. I believe the tree is a volunteer, and is blocking the view from the deck (so is a nuisance). I will cut it down in the spring and put some compost around the azalea. It's a small yard anyway and doesn't need that tree, however it got there.

fwiw, I had trouble with azaleas this year, presumably drought related. 3 of 5 of them really did poorly. They never really flushed out much if any new growth and struggled all season. One I had to pull it was so bad. Maybe the other two will come back next year, as will the one you posted about.

Azaleas (and rhododendrons) being grown in pots in peat based medium need their roots to be well disturbed (or better to be washed out of peat completely) before planting. Otherwise they'll strugle for years and may eventualy die.