Americans' ratings of the job the Centers for Disease Control, or CDC, is doing are down significantly from last year, whereas ratings of other key government agencies measured both years are the same or better.

Americans' views of the IRS have grown more negative since 2009 -- when Gallup last asked Americans to rate government agencies. Americans rate the IRS least positively of nine federal agencies, and the CDC and FBI most positively.

Slim majorities of Americans are closely following the situations involving the IRS (54%) and the congressional hearings on the attack on the U.S. consulate in Benghazi, Libya (53%), although most say both should be investigated.

Americans are more likely to believe that top officials in the IRS, as well as in the Obama administration, knew the IRS was targeting conservative groups, than to say awareness was limited to the branch office where it occurred.

Despite a generally negative view of the federal government, Americans soundly disagree with presidential candidate Ted Cruz's proposal to eliminate four departments of government and his proposal to abolish the IRS.

In 1975, Americans' image of the FBI was much less positive than 10 years earlier, following revelations about FBI surveillance practices.

The U.S. Postal Service ranks highest of 13 government agencies according to Americans' ratings of how well each is doing its job. Younger Americans, men and women alike, are more positive about the Postal Service than are older Americans.

Fifty-four percent of Americans say the federal government has too much power; 46% say it poses an immediate threat to ordinary citizens. Despite the controversies facing agencies like the IRS, both measures show little recent change.

For nearly a decade, the majority of Americans have perceived corruption as widespread in their government. In 2014, three in four saw extensive corruption -- up from two in three in 2007 (67%) and 2009 (66%).

As President Barack Obama prepares to make his State of the Union speech Tuesday night, here are several contextual considerations to keep in mind, from the perspective of the American people.