Freshman Sen. Rand PaulRandal (Rand) Howard PaulGOP senators call for probe of federal grants on climate change Overnight Health Care — Presented by the Association of American Medical Colleges — Key ObamaCare groups in limbo | Opioids sending thousands of kids into foster care | House passes bill allowing Medicaid to pay for opioid treatments US watchdog: 'We failed' to stem Afghan opium production MORE (R-Ky.), who offered the substitute amendment, said on Thursday that his plan was a much simpler way to deal with the possibility that some lawmakers could be engaging in underhanded investments. 

Lawmakers "would have to sign an affirmation each year that they did not participate in insider trading," said Paul. "This is a good way to do it without creating a bureaucratic nightmare that may have many unintended consequences."

In debate earlier in the week Paul said he did not believe that any of his colleagues were currently engaged in insider trading. He also pointed out that the underlying STOCK Act does not change law but only affirms that existing law affects lawmakers as well as business men who are not in government. 

Two of the STOCK Act's floor managers, Sens. Joe Lieberman (I-Conn.) and Susan CollinsSusan Margaret CollinsSenate Gang of Four to meet next week on immigration Republicans agree — it’s only a matter of time for Scott Pruitt Skyrocketing insulin prices provoke new outrage MORE (R-Maine.), immediately took the floor to oppose Paul's amendment.

"The affirmation … is in my opinion not enough … because it doesn't establish the duty of trust this underlying bill does," said Lieberman.