Why did the Federalists lose popular support during John Adams' presidency?
The Federalists lost popular support during John Adams’ presidency because John Adams was not George Washington and the Federalists’ ideology was not democratic enough for the tastes of most Americans.
The Federalist Party had been the party that promoted the Constitution of the United States as a replacement for the Articles of Confederation. This meant that it was suspicious of democracy and wanted government to be less responsive to the people. This was, of course, an ideology that was hard to justify in a country whose government was supposed to be based on the consent of the governed and the idea that all (white) men were equal to one another.
Although Federalist ideas were not very popular, the people were willing to be governed by them as long as George Washington was president. His personal prestige reassured people and it helped cause them to accept Adams as his chosen successor. However, once Washington was out of the picture, people were less willing to accept Federalist ideas. They felt that the Federalists were not democratic enough and that they even tended to prefer monarchy to democracy.
These worries about the Federalists were exacerbated by the passage of the Alien and Sedition Acts during Adams’ presidency. The Sedition Act, in particular, was very important. In essence, it made it illegal for people to criticize the government. The Federalists used this to do things like closing down newspapers that supported the Republican (aka Democratic-Republican) Party. When the Federalists did this, it made people even more suspicious of them. It made people suspect that the Federalists would not support American, democratic, values in the long term.
Basically, the Federalists’ ideas were no longer acceptable to most Americans. Their ideas were not sufficiently democratic. Moreover, they no longer had George Washington to lend them his personal prestige and to make them look good to the people. For these reasons, they lost popularity during John Adams’ presidency.