So the big scandal here isn't that the FBI is implicitly threatening Twitter in a way that raises 1st Amendment concerns, but rather that the FBI is using public funds to help a social media company do its job. This has nothing to do with free speech and there's also no evidence the FBI's actions were motivated by partisan concerns.
To me, it's rather clear that a bunch of people who are not particularly principled or have a strong understanding of the ethics or laws involved, but are prone to thinking that anyone working against their own agenda must be evil or nefarious in some ways, reverse-engineering their way into finding faults with how things more or less have always worked. This also isn't some nefarious hidden secret motivated by partisan concerns. Trump's own Director of FBI, Christopher Wray stated that Russia was attempting to interfere in the presidential election:
https://www.reuters.com/article/us-usa-election-security-idU...
> Russia is determined to interfere in U.S. elections despite sanctions and other efforts to deter such actions before the next presidential election in 2020, FBI Director Christopher Wray said on Tuesday.
And he specifically told the public what the FBI is doing about this:
https://time.com/5548544/russian-internet-trolls-strategies-...
> FBI Director Christopher Wray, speaking at the RSA Conference in San Francisco on Tuesday, said social media remains a primary avenue for foreign actors to influence U.S. elections, and the bureau is working with companies on the problem.
> “What has continued virtually unabated and just intensifies during the election cycles is this malign foreign influence campaign, especially using social media,” Wray said. “That continues, and we’re gearing up for it to continue and grow again for 2020.”