Do we know what the Watergate burglars were after?
After decades of silence on the Watergate break-ins the main characters have begun speaking; however, the explanations conflict. Beyond this their answer to the motivation behind the break-ins are self serving or vague. The two most creditable conspirators are John Dean and Stuart Magruder and their answers are given be low.
Explanations given by the main Watergate conspirators mostly conflict. Beyond that some are self-serving, nonsensical or incomplete. One watergate conspirator (Stuart Magruder) did confirm a explanation which was first proposed by the chief counsel on the Senate Watergate Committee and which is plausible and elaborates on the answer John Dean gave.
First the Self Serving:
Howard Hunt told the Miami Herald in 1997, that they were looking for financial links between Cuba, North Vietnam and the DNC
Ex-Spy Crafted Watergate, Other Schemes
“What we were looking for is the same thing every congressional committee is looking for today, which was evidence of illegal foreign contributions,” he told the Miami Herald in 1997. “That was the rationale for going in there. We’d heard rumors that both the Vietnamese and Fidel Castro were inserting funds illegally into the Democratic National Committee. And the idea was to look at the books, photograph them, in and out, and that’s it. It didn’t seem like such a deal to me. You know, I’d been doing that stuff for years, a ‘black-bag job’ into other embassies. But you know, I didn’t have skilled people.”
This is not plausible because if such treasonous activity were occurring it would have been the CIA and FBI who were conducting court ordered search and sezures and not the white house plumbers illegally breaking in. That Howard Hunt would propose this explanation is self serving because it means he was actually working on behalf of America's security rather than subverting it as part of rigging the 1972 election.
In 2001 G Gordon Liddy testified in court, the Watergate Breakin's were conducted to retrieve evidence of Prostitution at the DNC.
G. Gordon Liddy Gives First Testimony on Watergate Break-In
(Watergate) burglars were not seeking political intelligence but photographs linking the future wife of President Richard M. Nixon's White House counsel, John W. Dean III, to a call-girl ring.
G. Gordon Liddy
"Maxie" Wells, a former DNC headquarters secretary who sued Liddy for saying that the her desk was targeted in a search for pictures of prositutes by Watergate burglars. The case was dismissed by the U.S. District Court in Baltimore after jurors could not reach a verdict. Wells appealed that decision.
The reason this is self serving is because Liddy and John Dean have had a long and bitter feud based on their different approaches to the Watergate scandal. Liddy remained silent and for this received the harshest jail sentence of any of the conspirator (20 year sentence, served 8 with a Presidential commutation), John Dean cooperated with the prosecutors and was given a more lenient 4 month jail sentence and has been pilloried by Liddy ever since.
As previously mentioned in another answer John Dean in 2009 said the Watergate plumbers were seeking evidence the Democrats were engaging in potentially-illegal fundraising activities.
This is incomplete because he doesn't mention who the Democrats were suspected of receiving these funds from. How Nixon heard of these activities, and of coarse after years of investigations by congress no such "illegal" activities were uncovered.
Beyond that this explanation does dovetail into the last explanation which fills in the missing details.
Jeb Stuart Magruder
A Key White house aid, who later was appointed deputy Attorney General, who during the break in served as a middleman between the politicians (Haldeman, Mitchell, Nixon) and the plumbers (Liddy, Hunt) supports the most popular explanation. Magruder served 7 months in prison for his watergate actives, and in 1996 he confirmed an explanation first proposed by Terry Lenzner
chief counsel on the Senate Watergate Committee.
Why the Watergate Break-In?
The Nixon forces were trying to determine what Lawrence F. O'Brien, the chairman of the Democratic National Committee, knew about some shady dealings between Nixon and Howard Hughes, particularly $100,000 passed from the multimillionaire to the President's friend Charles (Bebe) Rebozo, part of which was apparently later spent on furnishings and jewelry for the President and his family. Secondarily, the White House may have been trying to dig up some dirt with which to persuade the Democrats to withhold, during the 1972 campaign, what they knew about the Nixon-Hughes relationship.
This makes sense because the target of the break-in was Lawrence O'Brien; who had previously worked for Howard Hughes and continued to have a good relationship with the Hughes organization. This relationship was a key point of paranoia for President Nixon who feared both evidence of Nixon's relationship with Hughes, and a possible Hughes financial relationship with the DNC.
Hughes money had helped resurrect Nixon's career after his first loss to Kennedy in 1960 campaign. They had since had a falling out; Nixon was paranoid that Hughes was backing the Democratic Candidate in 1972; and feared details of his previous dealings with Hughes would come out and be damaging.