Not willing to wait until the Democratic primary contests are officially over, a powerful outside group behind Hillary Clinton is moving up plans to attack Donald Trump, starting this week.

Priorities USA, which is known to have already accumulated an impressive $130m (£90m) war chest, will launch an intense round of TV campaign commercials slashing at the New York billionaire in several key general election battleground states on Wednesday.

The Super PAC had originally signalled that it would hold fire on the presumptive Republican nominee until after the last big day of primary voting on 8 June in California and New Jersey.

The decision to let loose now in the key swing states of Ohio, Florida, Virginia and Nevada reflects uneasiness in some Democrat corners that Ms Clinton may be more vulnerable to the Trump steamroller than they had originally thought was possible.

The group has been tightlipped about the content of the spots and whether they will focus on the policy differences between Democrats and Mr Trump – or, indeed, between him and his own party – or if they will bring out personal dirty laundry, for instance on his record with women.

“Donald Trump is a divisive, dangerous, conman who should never be president of the United States,” Justin Barasky, a spokesman for the Super PAC, told CNN. He conceded that the airing of the ads at this early stage, even before Ms Clinton has formally dispatched her rival for the nomination, Bernie Sanders, means that it is is preparing “for a close and competitive election”.

Since his remaining rivals in the Republican race surrendered, Mr Trump has basked in media attention, some positive, some perhaps less so. But recent national polls have put him neck and neck with Ms Clinton in swing states that could decide the general election in November.

He and his backers are, however, very far behind Ms Clinton in terms of getting their fundraising act together. While some conservative donors have in recent days signalled an interest in donating large sums to help the Trump cause, there is as yet no Super PAC ready to receive and spend the money. Indeed, formally Mr Trump still excoriates the whole nation of Super PACs.

“Mr. Trump continues to disavow all Super PAC’s,” Corey Lewandowski, the Trump campaign manager, said just this weekend.

Those with the chequebooks out and ready include Sheldon Adelson, the Las Vegas casino billionaire, who has said that he is ready to spend $100m helping elect Mr Trump as president. Still on the sidelines, however, are the billionaire industrialists David and Charles Koch, who once said they would spend $900m on this election.

But Charles Koch may have spoken for many in the wealthy conservative class when he wondered out loud recently if Ms Clinton would be a better bet than Mr Trump to run the country.

Camp Trump is so far behind in erecting a coherent structure for raising money, both raising money on its own behalf and then tapping the backing of Super PACs, largely because Mr Trump largely self-funded himself through the primaries. He has since indicated that he does not have the ability to do the same for the general election and there is little evidence he has the liquid assets to do so anyway.

The relative disarray on the Republican side will surely eventually be resolved, but in the mean time it provides an opening for the Democrats to get in early, which is exactly what Priorities USA has decided to do.

The start of the Super PAC's advertising effort is another signal of how the race for the White House has essentially already shifted into general election mode.