So . . ..
Either Clapper is lying again, or there's an alternative explanation.
The New York Times etc. have been reporting a narrative based on anonymous sources, a narrative which derives from the Obama Administration and which it wanted everyone to believe.
I say it's an "Oh look! A deer!" narrative. It was designed to get the bloodhounds off the trail and follow to an inconclusive nowhere.
The real story instead might be that Obama was using the Treasury Dept. to investigate Manafort, giving the FBI, CIA and the NSA the plausible deniability they have asserted. So far Comey and Clapper have denied any spying on Trump.
Well, the Treasury Dept. was involved according to news reports, but so far no one's asked Jack Lew to comment as far as I know.
It was Manafort's financial connections in Ukraine which the Times reported in the summer which caused Manafort to have to bail from the Trump campaign, and Bannon and Conway to be tapped by Trump in August 2016.
The spying on Trump by the Treasury Dept. might have then continued, quite lawfully, endeavoring to uncover evidence of Trump financial wrongdoing in connection with Russia, or some one else, in order to finish him off, but it failed.
Jack Lew served Obama at Treasury to the bitter end.
[T]he Inspector General of the Department of the Treasury shall be under the authority, direction, and control of the Secretary of the Treasury with respect to audits or investigations, or the issuance of subpenas, which require access to sensitive information concerning— ...
(E) intelligence or counterintelligence matters; or
(F) other matters the disclosure of which would constitute a serious threat to national security or to the protection of any person or property authorized protection by section 3056 of title 18, United States Code, section 3056A of title 18, United States Code, or any provision of the Presidential Protection Assistance Act of 1976 (18 U.S.C. 3056 note ; Public Law 94–524).