Moody’s Investors Service bumped Thornburg Mortgage late last month from its top-notch Ba1 rating down a tick to a Ba2 grade on the company’s $200 million of senior unsecured debt. The agency said the downgrade was motivated by expectations that Thornburg, of Santa Fe, NM, would be more highly leveraged than it originally had expected. Included in the rating action is Moody’s belief that Thornburg is shifting funding of its growing asset base toward