What you need to know about the 'deep state'

— -- The idea that a "deep state" exists inside the federal government has risen to prominence during the first 100 days of President Donald Trump's administration -- but what does it mean? And does it actually exist?

Those are the questions that top White House officials have hinted at during the first three months of Trump's tenure, and both conservatives and liberals are split on whether there is an organized effort among career bureaucrats to undermine the president's agenda.

Trump's chief strategist Steve Bannon is the most ardent believer in the White House that a deep state exists, telling conservatives earlier this year that the "deconstruction of the administrative state" was important to the new White House.

Here's what you need to know about the deep state.

What is the deep state?

"Deep state" is the term used to refer to the idea that there's a cadre of career employees inside a government are working together to secretly manipulate government policy and undermine elected leaders or political appointees. These people can have positions in the military or intelligence fields, as well as other areas of government like bureaucratic agencies.

Many write off the concept of a deep state in the United States as a mere conspiracy theory since no evidence of an organized effort has surfaced. But Trump supporters say that leaks to the media point to the possibility that government bureaucrats are trying to block Trump's agenda.

The term began gaining traction in the United States during the 2016 presidential race -- escalated by articles from the conservative publication Breitbart News, formerly led by Bannon -- and mentions became more frequent and prominent after Trump's election to the White House.

The phrase was originally used to refer to power dynamics in foreign countries like the former Soviet Union and countries where employees of former authoritarian regimes try to undermine newly elected leaders in fragile democracies.

It's highly unusual for a president of the United States to claim the existence of a deep state within his own government, publicly accusing employees within the executive branch of actively trying to undermine his agenda.

What Americans think about the deep state

A new ABC News/Washington Post poll from Thursday showed that nearly half of Americans believe there is a "deep state" operating within the federal government.

It was defined in the poll as “military, intelligence and government officials who try to secretly manipulate government policy.” A plurality -- 48 percent -- think the deep state exists, while only a third (35 percent) say it's only a conspiracy theory. One in six Americans say they don't know.

Twenty-eight percent say the deep state exists and that it's major problem.

Unlike most issues in today's divided political climate, belief in a "deep state" comes evenly from both parties. Forty-five percent of Democrats say there's a deep state and 46 percent of Republicans say the same. Fifty-one percent of independents believe the same.

Still, there's an age gap in belief in the deep state. Six in 10 people under 30 say they believe in the deep state, versus only 37 percent of seniors.

ABC News' Lindsey Jacobson and Gary Langer of Langer Research Associates contributed to this report.