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When the Jets signed cornerback Trumaine Johnson to a five-year, $72 million contract this offseason, the thought was he should come in and immediately improve the Jets’ defense. In a sense, he did, as he intercepted a pass in Week One. But since then, the results have not been pretty.

Johnson has been profoundly disappointing to people inside the organization, according to Manish Mehta of the New York Daily News, who quotes one source as saying, “Thought he’d be better.”

In fact, since that solid performance in Week One, the Jets’ defense has actually played better during the five games Johnson missed when he was injured. Many league observers believe Darryl Roberts, the minimum-salary backup who was starting while Johnson was hurt, has actually played better than Johnson this season. That’s despite the fact that Johnson will pocket $26 million in salary and bonuses in his first year with the Jets, while Roberts makes less than $1 million.

Johnson returned to the lineup on Sunday, moving Roberts to the bench, and the Jets promptly turned in their worst defensive performance of the season.

The 28-year-old Johnson looks like he’s not as good a fit in coach Todd Bowles’ defense as he was with what the Rams were asking him to do. That’s always a risk with a free-agent signing, that a player earns a big contract because he plays well in one situation, but doesn’t play well in the next situation.

Bowles is likely to be fired after this season, which means it’s going to be some other coach trying to get the most out of Johnson next year. Whoever that coach is, they’d better get the most out of Johnson. He’s set to cost $12 million against the Jets’ salary cap in 2019 and $15 million in 2020, and the way his contract is structured makes it virtually impossible for the Jets to move on from him until then. He still has time to get things turned around, but through his first half season with the Jets, he’s looking like an expensive mistake.