While Romney has his own confab for the super-rich, oil baron brothers hunker down in California with wealthy conservatives

Charles and David Koch, the secretive oil barons who are attempting to sway the 2012 presidential contest by injecting vast sums of private cash into the electoral process, have moved one step closer to achieving their goal by staging a gathering of right-wing donors in San Diego.

The brothers, who have set themselves up as a two-man attack machine devoted to unseating Barack Obama, held the latest of their twice-yearly summits of super-wealthy conservative funders this weekend.

Previous conferences have raised about $250m in private donations, putting the Kochs well on the way to their target of $400m for this election cycle – a flexing of individual political muscle by the super-rich never before seen in American history.

Details of the guest list and agenda at the luxury Carlsbad resort were sketchy, unsurprisingly so given the brothers' legendary secrecy.

Only rarely have glimpses been achieved into the rarefied world of these gatherings, in which wealthy conservatives meet to discuss how they can overturn normal democratic processes by leveraging their money into electoral races.

The only major breach of the security fortress they erect around their summits was in 2011, when advance notice of a Koch confab at the enclave of Rancho Mirage in the California desert allowed protesters to swarm the event.

Snippets of information collected over the years have revealed some of the top names among the Kochs' guests, who have included the US supreme court justices Clarence Thomas and Antonin Scalia; talk radio stars such as Rush Limbaugh and Glenn Beck; and prominent Republicans like Rick Perry of Texas and Chris Christie of New Jersey, who are both regular attendees.

This year the Kochs had competition – an unusual experience for them – as the presumptive Republican presidential candidate Mitt Romney staged his own shindig for super-wealthy donors in Park City, Utah.

His guest line up included that other powerhouse of conservative fundraising in this election cycle – the former George Bush adviser Karl Rove, who has also pledged to inject hundreds of millions of dollars into political campaigns this year through his Crossroads GPS group of super PACs.

Technically, there is no contact allowed under campaign finance laws between the non-party political fundraising efforts of the Kochs and Rove and the official campaign of Romney and the Republican party. But the cross-over of staff, supporters and issues makes the line between them very blurry indeed.

Taken together, Romney's official campaign and his outlying supporters could throw more than $1bn at their attempt to extract Obama from the White House and retake the US senate in November. Much of the money is being invested in negative TV attack advertising in key swing states.

The Kochs have also been working quietly behind the scenes to amplify their political influence by creating a vast database containing the details of potential Republican voters, known as Themis.

The database was believed to have been on exhibition at the San Diego summit this weekend.

Over the past five years, the Kochs have become a contentious force within American politics, partly because of the sheer resources they have at their disposal. The brothers, who made their money in oil, coal and manufacturing, have a personal wealth of $25bn each.

Their controversial role is heightened by the increasingly activist stance they have taken in recent years. They have a stated desire – expressed openly to their inner circle – to bend the political process to their individual will.

A leaflet sent to donors in 2008, obtained by one of the top Koch watchers in the US, Kenneth Vogel of Politico, warned that"our society faces dangerous and imminent threats".

It added ominously: "Can a small but dedicated group of leaders make a difference?"

The brothers have even caused fights within the core conservative movement.

On Monday, the Cato institute, a prominent libertarian think-tank, will announce that it has reached a settlement with them in a bruising fight for control.

The brothers had used the death of one of the Cato's four shareholders, William Niskanen, to launch a power grab for the institute, which was then fiercely resisted by senior Cato figures who feared the Kochs would reposition the organization to fit their own agenda.

The settlement appears to be a compromise. The Kochs will agree to give up their attempt to take over Niskanen's shares, which would have given them a majority stake, and in return the founder and president of Cato, Ed Crane, will stand down and be replaced by a successor that he will select – albeit with the Koch brothers holding an ultimate power of veto.

If they meet their target of $400m for this year's presidential election cycle, the Kochs will have surpassed the $370m that John McCain had at his disposal as his entire campaign funding in 2008.