Prediction: he'll take a plea. In mitigation, France is an ally. Aggravation: these are nuclear secrets. France will not come to his aid, as Israel did for Pollard for many years, unsuccessfully. Fortunately, there was no real harm. 20 years unless he gets a particularly harsh judge. Worst case: 40.
Even if France didn't care about the information being shared elsewhere, they would still likely care about potentially breaching the classified information treaty they signed with the USA back in 1977[1]. When France received the information, they may have assumed it was a test from the USA to see if France was still upholding their treaty obligations to report unauthorised distribution of US classified information?
[1] https://treaties.un.org/doc/Publication/UNTS/Volume%201114/v...
Makes a big difference to what, are you suggesting?
In the law? How does Russia vs France make a difference? we have declared war against neither. Sharing national security secrets with either is a crime in fact.
How it looks in the news and to the social media mob? Sure.
But there are two questions: how did the FBI find out about it? Was Toebbe targeted by an informant?
Secondly, which country was he offering the secrets to? This makes a big difference. "Enemy" or ally? Maybe he felt sorry for the way France was effed over by AUKUS and wanted to make amends.