It is noted that the president isn't sure about some of the document's aspects. In particular, he is wary of the fact that the law may limit the president's power, which is forbidden by the Constitution.
Trump also believes that the sanctions may hinder cooperation of the US with their allies.
As it was reported earlier, the US Senate has already signed the document. The bill includes both individual and sectorial sanctions against Russia, Iran, North Korea, and enshrines the already existing restrictions. It also deprives the US president of the right to cancel the sanctions without the approval from the Congress. Russia responded with reducing the diplomatic presence of the US in their country.