Just hours before his first address to a joint session of Congress on Tuesday, a cheery President Trump posed for pictures with roughly 20 Republican attorneys general. "These are some great people here," the president said – fully aware that the AGs are in the midst of filing a flurry of lawsuits against the Trump administration.

Why?

"Sometimes it turns out the best way to help President Trump ... is to sue President Trump," Missouri Attorney General Josh Hawley explained to Fox News.

Despite the unusual optics of all these lawsuits, the intention of Hawley and the other AGs is to use the suits to block federal regulations, mostly promulgated during the Obama administration but now in effect under Trump's.

In Missouri, this legal tactic centers on an endangered prehistoric fish that has outlived the dinosaurs, the Pallid Sturgeon. It reproduces in river shallows which have become fewer, due to the diking and channeling of the Missouri River. To resurrect the fish population, an Obama-era amendment to the Endangered Species Act allows the feds to designate as critical habitat areas where the fish may not even exist. The amendment was designed to expand ecosystems in order to maximize the endangered fish's ability to spawn.

But some landowners find the amendment intrusive. "This is the key part," said Hawley. "We are an agricultural state. That would mean farmers and ranchers could find themselves unable to farm their land, unable to develop their land." He said it's "absolutely a killer for small businesses and small farms in our state."

Hawley is one of 18 Republican AG's suing to overturn the rule. But they are combining forces to file other lawsuits -- challenging the Obama-era Waters of the United States regulatory plan, as well as overtime rules put in place by the Obama Department of Labor and the coal-crimping Clean Power Plan.

"In West Virginia, we suffered acutely because thousands upon thousands of people were put out of work. A number of those people left the state or are pursuing other employment," said Patrick Morrisey, West Virginia’s Republican attorney general.

Democratic attorneys general, meanwhile, also are mobilizing, trying to preserve Obama-era climate change regulations and, most recently, targeting Trump's travel ban. That multi-state attack worked, when Washington states Attorney General Bob Ferguson got a federal judge to temporarily block the policy nationwide. After the ruling, Ferguson noted, "We are a nation of laws. Those laws apply to everybody in our country. That includes the president of the United States."

AG's from both parties note filing lawsuits to overturn federal regulations is speedier than internal remedies -- the laborious and slow-moving federal rule-making process. They say the facts of the suits are usually well-known, testimony is usually limited, and judges tend to act quickly.

Republican attorneys general note there's an added benefit to them. The lawsuits are helping to restore the concept of federalism, empowering the states and restoring the balance of power against the executive branch.