Among them: A variety of provisions lawmakers included to force a more aggressive U.S. policy toward Russia. 

Those provisions, Trump said in his signing statement, raise constitutional concerns – and "could potentially dictate the position of the United States in external military and foreign affairs" and interfere with his ability to conduct diplomacy. 

The bill passed by Congress contains several provisions specifically targeting Russia. It restricts military cooperation with Russia, prohibits the United States from recognizing Russia's legal right to the disputed Crimea peninsula, and requires the military to "develop and implement a comprehensive strategy to counter threats by the Russian Federation" — including Russia's use of disinformation, social media and support for political parties.

Trump has himself expressed a willingness to work with Russia and touted his good relationship with its president, Vladimir Putin.