If we are talking about a government indulging in printing their own US currency then there are two issues with it:
For any large scale purchase or buying, they use marked currency of a certain series. Say, a country wanted to buy a few fighter jets or crude oil worth a few hundred millions then the recipient country would not only ask for marked currency but also verify the series to collaborate it with Fed to ensure copies of it are not in circulation.
Secondly, if a country wishes to sabotage another's economy then they would have to infuse it from Fed Reserve to banks. That's how new printed money is distributed. A foreign country can't make large scale disruption as it won't be able to infuse it to banks from the Reserve.