Through four weeks and four wins this season, there have been an awful lot of winners walking the Michigan sideline.

The most obvious winner has been sophomore sensation Denard Robinson who has captivated the nation and leads the NCAA with 688 rushing yards. Robinson’s performance has also shone a light on the team’s primary wideouts — Roy Roundtree, Darryl Stonum and Martavious Odoms — who have all come alive at some point or another in non-conference play.

Even Michigan coach Rich Rodriguez, who was vilified for the better of eight months before the season began, has proven that “winning cures a lot,” just like he said a month before the opener. He’s probably enjoyed a great deal more sleep in the last month than he had through the entire offseason.

But for all of Michigan’s shiny results through a third of the season, there’s been one lemon along for the ride. And winning may not cure enough to save his job.

Defensive coordinator Greg Robinson, in his second year running the defense, has done little to prove that he deserves to be off the hotseat, which he and Rodriguez shared at the start of the season.

Since year one of Rodriguez’s tenure, the Wolverines’ defense has been slowly decaying.

Under Scott Shafer — who was first brought to Ann Arbor by Rodriguez — Michigan gave up a fairly putrid 366 yards per game. Although a 3-9 record may have had something to do with it, Shafer was fired without many questions after the season.

After fielding one of the worst teams in the FBS in 2008, Robinson was removed as head coach of Syracuse and hired by Rodriguez to lead the Wolverine defense. The results he yielded in his first season were 27 yards worse than Shafer’s defense. And he was kept on.

And four games into his second season, the results have been even worse. Robinson’s defense was crushed for 535 yards against Notre Dame—the second-highest in a win in program history. Then, the week after, the Wolverines gave up 439 yards to an FCS squad that the defense was absolutely ill-prepared for.

The Wolverines are the second worst defense among undefeated teams in the FBS (only Oklahoma is worse), and overall, they come in at a stunningly awful 90th place in total defense, allowing 400 yards per game.

That’s not acceptable, unless you’re playing your buddy on Playstation.

And don’t blame it completely on a lack of talent. Yes, the secondary was expected to struggle because depth at the position group was paper thin. But at positions like linebacker (which Robinson personally coaches), Robinson’s unit has underachieved on a consistent basis.

For comparison’s sake, Shafer, who left town for Robinson’s old home in Syracuse, has the 29th-ranked defense in the FBS, while his defense is allowing almost 100 yards less than the Wolverines have on average.

That means only one thing with three quarters of the season remaining: Greg Robinson has the most to prove of anyone in Ann Arbor when Big Ten season starts next Saturday.

To say Rodriguez needs to fire Robinson to save his job, like ESPN analyst Mark May said following Michigan’s win over Massachusetts, is unfounded and untrue. But when it comes time to evaluate this team’s coaching staff at the end of the season, there should be a long look at Robinson’s track record through two years with the program.

When Athletic Director Dave Brandon was asked this offseason how Rodriguez could keep his job, Brandon said that he didn’t need to win a certain amount of games, but he needed to demonstrate a significant improvement and step in the right direction. There’s no reason why Robinson shouldn’t be held to the same standards.

So far Rodriguez, helped by his record-breaking offense, is on his way to doing that and Robinson is eating his dust.

While the defense showed some improvement this past weekend, consider the word out: If Greg Robinson doesn’t show noted improvement in Big Ten season, there’s no reason why his bags shouldn’t be packed.