Anonymous dissent has no credibility. Moreover, the dishonor of it undermines the character of the writer. A real dissenter would use his reputation and the status of his high position to lend weight to his dissent.
The New York Times' claim to have vetted the writer also lacks credibility, as the New York Times has consistently printed extreme accusations against Trump and against Vladimir Putin without supplying a bit of evidence. The New York Times has consistently misrepresented unsubstantiated allegations as proven fact. There is no reason whatsoever to believe the New York Times about anything.
Consider also whether a member of a conspiracy working "diligently" inside the administration with "many of the senior officials" to "preserve our democratic institutions while thwarting" Trump's "worst inclinations" would thwart his and his fellow co-conspirators' plot by revealing it!