Which decade saw a marked decline in american attitudes toward government?

It was the decade of the 1970s.

Explanation:

The main reason for this decline in public attitudes toward government was the Watergate Scandal. President Richard Nixon, a Republican, ordered the spionage of the Democratic electoral campaing in 1972, the year he was reelected.

Later, he denied any involvement and tried to obstruct a congressional investigation of the issue. The ilegal action was first reported by The Washington Post and its reporters Bob Woodward and Carl Berstein. Nixon refused to release his secret recordings at the White House and had to do it until the Supreme Court order the Presidency to do so. Then the truth was known, Nixon had known about the issue all of the time. Congress got ready to impeach him and he resigned on August 9, 1974 before becoming the first president to be impeached by Congress in US history. This issue severely undermined citizens' trust in the office of the Presidency.