Basically, Bud Elliott of SB nation (their recruiting beat writer) thinks that Harbaugh needs to "actually win some big games" otherwise recruiting could/will implode a la Brady Hoke following 2013.
Michigan did not sign a top-100 prospect in the class of 2018, and the 2019 class hasn’t has a top-200 player commit this calendar year.
... recruiting against Michigan right now is pretty easy: Harbaugh has never won the Big Ten East. He’s never even finished second. He has two ties for third and, most recently, a fourth-place finish.
His offense has been a disappointment. Michigan’s finishes in yards per game so far under Harbaugh are 105th, 58th, and 69th.
An honest assessment of the 2018 roster reveals a deep, talented team primed for a bounce-back. Almost all of the players on this roster were recruited by Harbaugh. It’s go time. If Michigan can go 9-3 or 10-2 in the regular season and win its bowl game, then Harbaugh’s 2017 really will look like a blip compared to 10-win seasons in 2015, 2016, and 2018.
Beating the teams on the field against whom Michigan recruits would really help.
Penn State’s recruiting is on a big roll. Ohio State might sign the No. 1 class in the nation. Wisconsin is putting together its best recruiting class in recent memory.
Harbaugh is 0-3 against Ohio State, 1-2 against Michigan State, 2-1 against Penn State, and 1-1 against Wisconsin. All four are on the schedule this season, as is Notre Dame.
Winning a conference title wouldn’t hurt either. Harbaugh finished second in the Pac-10 twice at Stanford, but has never won an FBS conference.