This isn't news. Here are some excerpts from "Kissinger and Nixon in the White House" an article by Seymour Hirsch in the May, 1982 issue of The Atlantic.

… Nixon was most anxious about the Brookings Institution, a liberal think-tank in Washington to which Mort Halperin had gone after leaving Kissinger's staff. Also at Brookings was Leslie Gelb, who, many in the White House believed, was involved in the Pentagon Papers leak to the Times. At one point during the meeting, prosecution files show, Nixon and Kissinger spoke of the possibility that other top-secret documents were stored in Halperin's or Gelb's safe at Brookings, awaiting future release. "They've got the stuff over there," Nixon said. "Stuff that we can't even get out of there from the Pentagon." Kissinger responded: "Can't we send someone over there to get it back?"

No attempt was actually made by the White House to get access, legally or by other means, to the documents believed stored by Halperin and Gelb, although many plans—including a proposed fire-bombing—were discussed over the next few weeks.

… Over the next two months, there was repeated and serious talk inside the White House of a possible fire-bombing of Brookings in an effort to steal the classified papers believed to be stored there. The project eventually came to the attention of G. Gordon Liddy, the former FBI agent, and E. Howard Hunt, the former CIA operative, who had been hired, with Ehrlichman's eventual approval, to work in the Plumbers unit. In his memoirs, Liddy wrote that he and Hunt developed a plan in September to buy a used fire engine and firemen's uniforms for a squad of Cubans who would be trained in fire-fighting techniques "so their performance would be believable." Brookings would "be firebombed" with delayed-timing devices; the Cubans would respond, "hit the vault [where Nixon believed the documents were held], and get themselves out in the confusion...." The plan was rejected as being too expensive, Liddy wrote. (All of this scheming took place after Liddy, Hunt, and the Cubans had broken into the Beverly Hills office of Dr. Lewis J. Fielding, Ellsberg's psychoanalyst, in a futile effort to find Ellsberg's psychiatric records or other possibly detrimental information….