A spokeswoman for the senator said Harkin is proud of his wife's financial success.
"Most of the assets reported by the Harkins have been made possible by Ruth's private-sector work," spokeswoman Kate Frischmann said in a statement.
"He views their life partnership as crucial to his own career, but his policy and political views are his own, as are hers. His policy views have not been guided by personal financial interests. Nor have his actions as a Senator, or information gained as a Senator, guided business dealings."
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Bobbye Pratt contributed to this article.