U.S. Sen. Bernie Sanders urged immediate action on limiting access to firearms following two mass shootings last weekend.

In an interview with the Des Moines Register before a weekend sweep in Iowa, Sanders endorsed a variety of measures intended to stem gun violence, including background checks, closing rules that allow anonymous trades and banning assault weapons. He also called for heavily licensing some weapons.

"Banning the sale and distribution today won't solve that problem (of weapons already in circulation)," Sanders said, noting there are 5 to 10 million assault rifles in the country now. "What we have to do is what was done back in 1986, when Ronald Reagan was president. What they said then, Congress and Reagan, was that we need to heavily license machine guns. Right now, very few people own machine guns as a result of that. We've got to very heavily license assault weapons, right now."

Sanders, who is seeking the Democratic nomination for president, planned to spend his weekend in Iowa hammering his signature "Medicare for All" proposal while hearing about health care issues specific to rural areas.

Then mass shootings in El Paso, Texas, and Dayton, Ohio, happened within 24 hours of each other. Thirty-one people died in the two incidents. The shootings changed Sanders' and other presidential candidates' plans and focus in Iowa.

Everytown for Gun Safety quickly organized a forum and started inviting the presidential candidates in town for the Iowa State Fair. Sanders rearranged his schedule, canceling one event and rescheduling another. Seventeen candidates plan to stop in at the all-day forum.

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"We were asked to do it, and of course, we have to do it," Sanders said. "Iowa, Vermont, the whole nation is reeling at the horrible, horrible events that we saw in El Paso, Dayton, and have been seeing for the last several years."

President Donald Trump has called for background checks, with the National Rifle Association's input, and "red flag" laws to force gun owners to temporarily hand over their weapons if someone who can access them is deemed a threat to themselves or others.

Sanders said Republican leadership is "simply too cowardly to stand up to the NRA," and that he'll ask Senate Majority Leader Mitch McConnell to reconvene the Senate so lawmakers can debate gun-related proposals.

Sanders downplayed criticisms that red flag bills could set up confrontations between gun owners and law enforcement. Instead, he said the laws could be a source of outreach to people at risk of harming themselves or others, or being victims to it.

"What the American people want now is action," Sanders said. "This is an enormously difficult issue. No one has any magical answers. As I said before, you have 300 to 400 million guns out on the streets right now. The American people want a look at a variety of approaches that can lessen the likelihood of mass killings and just gun killings in general. You have to take a look and have that discussion."

Sanders said he'll still trumpet "Medicare for All" at as many forums he can. As he started his trip in Iowa, he released a letter addressed to the heads of health insurance and pharmaceutical industry groups asking how much money they intend to spend fighting Medicare for All, and arguing that money could be used on health care costs, instead.

"Today we pay the highest prices in the world for health care, and we pay the highest prices in the world by far for prescription drugs," Sanders said. "What these guys will be doing is taking hundreds of millions of dollars out of health care in order to defeat the growing support we have for Medicare for All, and that is an outrage."