Letter: Trump's leaks to Russia are a criminal offense
Sean Spicer had the right to quit his job as presidential press secretary. President Trump had the right to fire him. The media have devoted a lot of time to their and others' probable reasons for disenchantment when they should be devoting time to more important issues, such as President Trump's giving important information to Russia.
Trump claims he had the right to declassify it. He didn't declassify it. He leaked it. More significant, whether or not the material was classified at the time, his action was criminal.
Using Google, it isn't hard to find 18 U.S. Code 794. It says that whoever, with intent or reason to believe that it is to be used to the injury of the United States or to the advantage of a foreign nation, communicates, to any foreign government, or citizen thereof, information relating to the national defense, shall be punished by imprisonment for any term of years or for life (or death, under some circumstances).
This should be brought to the public's attention, in case President Trump manages to have Special Counsel Robert Mueller and all his staff fired.
In addition to having violated 18 U.S. Code 794, it is likely that Trump violated the classification rules. I could not find these rules online, but it is a very good guess that there are specific procedures for declassification, that many people with appropriate clearance would know whether these procedures had been followed, and that President Trump did not follow them.