"it will hamper our investigation"
Well boo hoo. We have checks and balances and due process for a reason. It isn't about catching the bad guy at all costs.
Borders are in place to hamper agents. That is their whole purpose.
Crossing borders without permission is provoking conflict and war.
Crossing borders traditionally requires negotiation. This is the way in any governance framework.
A world without any respected borders is a world in which there is no escalation, protection and where government is melting down. An agency that is tasked with protecting the borders of the law should understand that. If anyone struggles just think how it feels (for the sake of the argument here it is irrelevant whether true or not) to be at the receiving end of Russian cyber bullying interfering with the election.