Barack Obama has moved swiftly to put his stamp on the Democratic party, announcing on day two of his status as presidential nominee that the central party will abide by the same rules on accepting money from lobbyists as his own campaign.

The move signalled that Obama intends to impose a new approach to politics, and that he wants to be seen to be doing so. A central theme running through his bid for the Democratic nomination is that he will sweep aside the chummy relationship between politicians and lobbyists and free himself from the grip of special interests.

Under the new rules, the Democratic National Committee, which raises central funds for the presidential campaign, will take on board Obama's existing ban on donations from lobbyists who do business with the government as well as from political action committees - private interest groups set up to raise money in order to influence the outcome of elections.

Apart from highlighting Obama's determination to be a decisive party leader, the imposition of tighter funding rules allows him a clear line of attack against his opponent, John McCain. The Republican has been beset with troubles over lobbying, despite his reputation as a scourge of special interests having initiated legislation in 2002 to clean up political campaign finance. McCain's advisers are prominent lobbyists. The senator for Arizona was forced to dismiss several after his campaign was criticised for employing two aides from a firm that has worked on behalf of the Burmese regime.

The other in-built benefit of moving quickly on campaign funding is that it will cost Obama very little. He has already established a phenomenal money-raising machine, largely through small donations achieved through the internet.

The Obama campaign has raised $272m (£136m). Considering the $200m donated to Hillary Clinton's fund - and presuming her supporters put their financial clout behind Obama's presidential hopes - McCain's available cash is dwarfed. In the primaries Obama spent more on television ads than Republicans combined.

McCain's weaker fundraising potential has forced him to accept about $84m in public financing, but with that comes overall spending limits. As the Politico website pointed out, Obama could outdo that several times over without having to draw on any public money. If a million of his 1.5 million donors contributed the legal amount of $2,300 each, he would have a war chest of $2.3bn - far in excess of anything ever seen in US political history.

With the Democratic nomination settled, the Republicans have been seeking to exploit divisions within the party and peel away Democrats and independents uneasy with Obama. The Republican national committee's research arm began releasing memos highlighting criticism of the Illinois senator from fellow Democrats as soon as he clinched the nomination .

They featured primary-campaign comments critical of Obama from former president Jimmy Carter, senators Joe Biden and Chris Dodd, former Iowa governor Tom Vilsack, and Hillary Clinton. The Republicans hope to capitalise on dissension among the 17.5 million Americans who voted for Clinton and show independent voters that not even the Democrats are united behind Obama. "The longer the Democrats have [to take] to heal these divisions, the longer it gives McCain to organise in the key states," said David Johnson, a Republican strategist. "It keeps them from attacking him and trying to tie McCain to Bush. If his own party has so many questions about him, how can the American people support him?"

Bruce Buchanan, a political scientist at the University of Texas, said Republican efforts are aimed largely at the blue collar voters Obama failed to win over. Those voters are mostly moved by economic issues. On those Clinton was seen as the stronger of the candidates, even though hers and Obama's policy positions were similar.