You should review your source, because according to the Director of the FBI James Comey, in his statement about the investigation into Hillary Clinton and her email. He explicitly says as a part of their investigation they looked into the accusation that she directed her staff to remove headings and portions marking information as classified.
They did not find that it happened. Ever.
You can read it here: https://www.fbi.gov/news/press-releases/statement-by-fbi-director-james-b-comey-on-the-investigation-of-secretary-hillary-clinton2019s-use-of-a-personal-e-mail-system
As to intent- yeah, intent is a important part of that law. Did he intend to share classified information over the channel?
That he did it points to a lot of "yes." What's important here is all of the very public statements made by a majority of the participants in that chat about the need for information security from the 2016 campaign. Here's the quote: Pete Hegseth in 2016: "How damaging is it to your ability to recruit or build allies with others when they are worried that our leaders may be exposing them because of their gross negligence or their recklessness in handling information?"
You can watch him say it here on Twitter: https://x.com/MattGertz/status/1904238661174018534?
So, if this were 2015, there's be a lot more benifit of doubt- maybe they didn't understand the risks and all of that. But this is a decade later. A decade of "but her emails." and the need for information security from the very people in that chat.
They all knew better and they did it anyway. From Vance on down, every single one should have been forced to resign that day.
What else have they been doing over Signal? That can't be the only chat they had going on. They have that chat a very specific title. If that was the only chat, why that specific title?