Mitt Romney's campaign has taken $4.3m in donations since the supreme court's decision to uphold Barack Obama's healthcare reform.

The Republican nominee's team is citing the influx of cash as a sign that the party base has been energised by the decision and that the issue will play a central role in November's White House election.

Romney's spokeswoman, Andrea Saul, said the $4.3m had come from 43,000 individual donors.

Many right-wingers, in particular the Tea Party movement, have been hesitant about support for Romney because he introduced similar healthcare reforms when he was governor of Massachusetts. With the supreme court option closed off, some may now see a Romney presidency as the only way to block Obama's health reforms.

Romney and Congressional leaders such as John Boehner and Mitch McConnell were careful to avoid expressions of disappointment in the wake of the ruling. But one of Romney's early rivals for the Republican nomination, Michele Bachmann, admitted outside the supreme court she was "profoundly disappointed".

Republican Congressman Mike Pence, at a closed door session of House Republicans, went much further, comparing the ruling to 9/11, a comment for which he later apologised, saying he did not mean to minimise the suffering of those who suffered from the terrorist attack.

It would have been so much easier for Congressional Republicans and Romney if the supreme court had ruled against all or part of the law. Obama would have been left vulnerable, sitting in the White House amid the wreckage of his flagship legislation, trying to work out which bits were salvageable.

Romney, campaigning in Virginia earlier this week, offered an advance of the line of attack he would have been taking: that Obama had squandered the first – and perhaps only – term of his presidency on a lost cause. "If Obamacare is not deemed constitutional, then the first three-and-a-half years of this president's term will have been wasted on something that has not helped the American people," he said.

But this Plan A had to be scrapped when the supreme court issued its ruling. Instead, Romney had to resort to Plan B, saying that he would do what the court failed to do and move to scrap it on the first day of his presidency.

Speaking in Washington, in front a podium decked with the slogan 'repeal and replace Obamacare', Romney said: "Help us defeat Obamacare. Help us defeat the liberal agenda that makes government too big, too intrusive, and is killing jobs across this great country."

The Romney campaign team claimed the supreme court ruling had galvanised the support of opponents of the law and that in the first three hours after the ruling $1m in donations poured into the Romney headquarters. The team will be hoping the supreme court move might rekindle the Tea Party movement, diverting its energy behind his campaign.

Romney will fight the election on healthcare but nowhere near to the extent to which he will on the economy, the issue which both he and Obama acknowledge will determine the outcome.

The health issue is no longer as big a positive for Romney as it was for the Republicans in the Congressional elections in 2010. Most voters have made up their minds, so there do not seem to be new votes to be won over. The crucial difference is that many of those opposed who profess to be opposed to the act want to keep some of the measures.

There are practical problems too with repeal. Although Romney said he would act to repeal Obama's Affordable Care Act from day one of his presidency, that is near impossible. There is almost no chance of the Republicans securing in November the 60 seats in the Senate they would need to prevent the Democrats from filibustering any attempts to repeal the legislation.

An alternative for Romney, and one he has described on the campaign trail, would be to try to wreck Obama's healthcare reform – or at least some of it. One way to do that would be to issue waivers to states allowing them to opt out.

But wrecking the reform is not as easy as it would have been two years ago. Romney and the Republicans would face a pushback if they tried to reverse some of the more popular measures.

What is telling from Romney's statement on Thursday is recognition that the outright hostility expressed two years ago is being replaced by this more mixed response. Among measures that are popular are forcing insurance companies to cover people with pre-existing conditions.

Instead of a complete denunciation of Obama's healthcare reform, as Republicans would have done two years ago, Romney devoted a large section of his statement to the parts he would keep. "What are some of the things that we'll keep in place, and must be in place, in a reform, a real reform, of our healthcare system?" He vowed to "make sure that those people who have pre-existing conditions know that they will be able to be insured and they will not lose their insurance".

The House Republicans, working in tandem with Romney, are to hold a vote on July 11 to repeal the Affordable Care Act. But it a purely symbolic gesture as the Democrats still control the Senate and even if they did not, Obama would veto it anyway.

Romney has not had a good few weeks. He has been outmanouvered by Obama on immigration reform. He has been forced on the defensive again over his time with Bain Capital because of a damaging Washington Post story about American jobs being sent overseas. His campaign team went to see the Post staff on Wednesday to rebut it but the Post stood by its story. Figures on Thursday also show an improvement in house prices, a hopeful economic indicator for Obama. But it was the supreme court that delivered the worst setback.