Supreme Court case on vindictive prosecution
The Supreme Court just handed down Hartman v. Moore. A quick read indicates that plaintiff engaged in a powerful lobbying campaign to get Postal Service to adopt a new technology, and was then indicted on kickback allegations. At trial, charges were dismissed for lack of evidence. Plaintiff sued, alleging that the prosecution was a "payback" for its lobbying, which was First Amendment protected.
The Supremes ruling: (1) the prosecutor is absolutely immune and cannot be sued, period (pretty much standard law); (2) where the government retaliation is something other than a criminal prosecution, it is enough to show that the government action would not have occurred except for the constitutionally protected act ("but for" causation); (3) but where the retaliation is a criminal prosecution, plaintiff must show that PLUS lack of probable cause ("strong suspicion" that an illegal act occurred). Since lack of probable cause = ground for suit for false arrest anyway, this makes a retaliation suit in a prosecution context a bit more complicated than false arrest, rather than simpler.
I suppose I can see both sides of the question, but it does illustrate that suing the government, even when it is punishing a first amendment exercise, is rarely a simple thing.