Why national emergencies are usually declared

President Trump's decision Friday to declare a national emergency is the latest in a series of emergencies that are used for international crises or urgent domestic dangers.

Why it matters: Most experts agree that Trump's use of a national emergency is a legally questionable use of emergency powers. The Brennan Center for Justice has found 123 emergency powers the president can invoke. There are one or two powers that Trump could use that are related to military construction.

• Those emergency construction powers have only been used twice: by George H.W. Bush during the Gulf War and then by George W. Bush after 9/11. Those orders aren't listed in the graphic because they were just amendments to earlier emergency declarations.

The backstory: Over the past 40 years, the National Emergencies Act has become a common tool for U.S. presidents to quickly enact foreign sanctions, especially when their views conflict with Congress. Of the 58 national emergencies in the data, 44 have been foreign sanctions.

Some examples:

• During the Iran hostage crisis, Jimmy Carter declared an emergency that's still active today, freezing Iranian government assets held within the U.S.
• Bill Clinton targeted the assets of individual drug traffickers and those who assisted them in Colombia.
• In response to human rights abuses in Venezuela, Barack Obama targeted high-ranking officials and their assets.

Other uses of emergency powers:

• In response to clashes between U.S. and Cuban vessels, Clinton invoked a power allowing the Transportation Department to better regulate the movement and inspection of ships.
• During the H1N1 virus outbreak in 2009, Obama allowed the Department of Health and Human Services to modify or waive some Medicare, Medicaid and CHIP requirements to implement emergency plans.
• To stop the proliferation of weapons of mass destruction, Clinton empowered the Commerce Department to control any exports that could aid countries in producing those weapons.

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