Five years have passed since the Federal Housing Finance Agency filed suit against 18 Wall Street firms and banks for peddling nonprime MBS to Fannie Mae and Freddie Mac in the years leading up to the housing crisis. All of the defendants have settled or lost with one glaring exception: Royal Bank of Scotland. As for when (and if) RBS will settle, that’s a different and complicated matter. The bank is presently owned by the British government, which took control of it during the financial crisis. In other words, any settlement might entail taxpayer money and cause a political controversy in the U.K. And the bill could be...