Serious questions emerging about the behavior of Representative Michael Grimm, Republican of New York, deserve a thorough inquiry by the Office of Congressional Ethics and the Department of Justice. Mr. Grimm, who highlights his previous service in the military and the F.B.I., denies any wrongdoing. But a detailed tracking of his campaign fund-raising activities by The Times has uncovered a pattern of donations that, as described by donors, would be illegal for exceeding federal limitations, or being paid improperly in cash, or coming from foreigners barred from giving.

Mr. Grimm has also shown decidedly poor judgment in his choice of backers and friends. When he first ran for the House, two years ago, his campaign collected more than $500,000 from followers of Yoshiyahu Yosef Pinto, an Orthodox rabbi and mystic from Israel. Mr. Grimm’s main contact with the group was Ofer Biton, a top aide of the rabbi, who is now under investigation by federal prosecutors over accusations that he embezzled millions of dollars from the rabbi’s congregation. Several of the rabbi’s followers interviewed by The Times said Mr. Biton aggressively sought donations for Mr. Grimm in hopes that he would be able to get an immigration green card once Mr. Grimm was in office. One donor, speaking anonymously to avoid involvement in the investigation, told The Times Mr. Grimm had him hand over $5,000 in cash during the 2010 campaign; another told of repeated demands from the candidate for thousands of dollars beyond legal limits.

There are also worrying questions about Mr. Grimm’s business dealings with another former F.B.I. agent who served 18 months in prison for business fraud. Mr. Grimm has said he was only helping “a friend that needed a hand.”

Donors’ allegations about the Grimm campaign raise questions of possible violations of “straw donor” laws against fictitious contributors. It is important to note the congressman’s insistence on his complete innocence, while declining to answer detailed questions. Those questions should be thoroughly pursued by proper authorities.