If the IRS can collect taxes from expatriate US citizens living and working overseas, the federal courts can certainly prosecute US citizens for breaking other federal laws while abroad.
Otherwise, those people might as well wipe their backsides with their Form 2555s and mail them back without checks attached!
And that's before you even consider the willingness of US courts to prosecute foreign nationals for breaking US laws on foreign territory, where one or more US citizens may have been tangentially affected by it.
Law enforcement cannot be above the law. It destroys the principles that make laws worth having and enforcing.
Congress is capable of enacting laws with extraterritorial reach. I am unaware of any law that should be interpreted to criminalize the NSA's international spying.
then there Article 2 Section 8 which does not grate the authority to create and agency such as the NSA or preform international Spying thus since the constitution does not expressly grant such authority the Federal Government is barred from such activity
Otherwise, those people might as well wipe their backsides with their Form 2555s and mail them back without checks attached!