MILWAUKEE — Nearly as many Americans die from guns as from car crashes each year. We know plenty about the second problem and far less about the first. A scarcity of research on how to prevent gun violence has left policymakers shooting in the dark as they craft gun control measures without much evidence of what works.

That could change with President Barack Obama’s order Wednesday to ease research restrictions pushed through long ago by the gun lobby. The White House declared that a 1996 law banning use of money to “advocate or promote gun control” should not keep the Centers for Disease Control and Prevention and other federal agencies from doing any work on the topic.

Obama can only do so much, though. Several experts say Congress will have to be on board before anything much changes, especially when it comes to spending money.

How severely have the restrictions affected the CDC?

Its website’s A-to-Z list of health topics, which includes such obscure ones as Rift Valley fever, does not include guns or firearms. Searching the site for “guns” brings up dozens of reports on nail gun and BB gun injuries.

The restrictions have done damage “without a doubt” and the CDC has been “overly cautious” about interpreting them, said Daniel Webster, director of the Center for Gun Policy and Research at the Johns Hopkins Bloomberg School of Public Health.

“The law is so vague it puts a virtual freeze on gun violence research,” said a statement from Michael Halpern of the Union of Concerned Scientists. “It’s like censorship: When people don’t know what’s prohibited, they assume everything is prohibited.”