MBS prices fell by roughly 100 basis points this week, but the downdraft could be short-lived thanks to the European Central Bank, according to MBS analysts and other market watchers. Late this week, the ECB cut its main interest rate to a record low 15 basis points, from 25 basis points. But in an unprecedented move, it also trimmed the interest rate it pays to banks on reserves to negative 0.1 percent. The move into negative rate territory is meant...