It's like he went out of his way to pick the worst most damaging possible choice.
The traditional U.S. intelligence partners (Australia, Canada, New Zealand, and the United Kingdom) will not be able to trust the U.S. anymore if she is in charge of intelligence. They would be completly justified in cutting the U.S. out of the traditional group. That is why her confirmation is a threat to national security (among other things such as her being a Kremlin propaganda repeater).
There are other very bad picks remaining now that Gaetz is out, of course RFK Jr. and nominated defence secretary Fox News guy.
But I think the confirmation of Gabbard would be the most consequentially dangerous one of all the bad picks.
Can Russia’s ‘girlfriend’ Tulsi Gabbard keep US secrets? - CSMonitor.com