I don't necessarily think Iowa's defense has "declined" per se, but when your offense and special teams gifts the other teams with turnovers and/or favorable field position, it suddenly makes it a lot easier to score points. Iowa has been caught with its pants down more than once this season, and it paid for it more often than not. The Wisconsin game is one I'm sure the Hawks would love to have back.
Iowa's run game hasn't exactly taken off this season. Normally it's the bread-and-butter of Iowa football, but part of it is the run blocking isn't quite up to snuff, and part of it is that Iowa doesn't have a top-notch tailback. The passing game has certainly kicked it into another gear so that's something, but it's still a bit hot-and-cold.
I'll admit I don't know a ton about UMD, but they appear to have a strong running game, and a strong run defense. I do think that's good news for Iowa, but Maryland probably is the most athletic team Iowa faces all year (with the exception of Penn State). I think the double-digit line is a bit much, I think it should probably be closer to 6 or 7. I'm just glad the game is at home.