The Supreme Court’s much-anticipated ruling on healthcare, expected in late June, may have one surprising outcome: A modest impact on President Barack Obama’s re-election bid, even though he is intimately associated with the challenged law

That wouldn’t be the case if anyone other than Mitt Romney were Obama’s likeliest Republican challenger this autumn. Romney, however, is singularly ill-positioned to capitalise on the issue because he championed a similar healthcare law as Massachusetts governor in 2006.

It’s a political dilemma that some Republicans – chiefly Rick Santorum – have been raising for months. It gained sudden urgency this week, as Romney continues his slow but steady march toward his party’s nomination and the Supreme Court’s conservative majority expressed pointed scepticism about the federal healthcare law’s constitutionality.

At least one of the five most conservative justices on the nine-person court must vote to uphold the 2010 Democratic-crafted health law for it to remain in place and continue its phased-in changes to current policies. Some independent analysts were struck by the seeming hostility of questions from conservative justices, and several now predict the court will overturn the law this summer.

Such a legal bombshell in the middle of an election year would have hard-to-predict impacts on the liberal and conservative bases of the parties and on House and Senate races. Leaders of both parties, however, say the effect on the presidential race will be muted, at least in part, if Romney secures the Republican nomination, which he is on track to do.

“Gov. Romney was so much involved in creating just about this exact law that his attacking it now is going to have virtually no credibility,” Democratic Sen. Chuck Schumer of New York told reporters.

Santorum has made similar claims in his plucky but underfunded presidential bid. Talking about healthcare on Sunday in Wisconsin, the former Pennsylvania senator said Romney is “the worst Republican in the country to put up against Barack Obama”.

Santorum cooled his rhetoric only slightly in a statement yesterday. He said the 2010 healthcare law “is a dangerous precedent and should be repealed in its entirety. Mitt Romney is the author and champion of Romneycare, which possesses many of the same features as Obamacare – including an individual mandate.”

Romney’s 2006 Massachusetts law required residents to obtain medical insurance or pay a fee into the healthcare system. The goal, he said, was to stop people from exploiting the medical industry by showing up for uninsured care at hospital emergency rooms, which had to spread their costs to other residents.

Obama cited the same need to deal with “free riders” in his push for a national healthcare overhaul, which became bitterly partisan and gave birth to the limited government, anti-tax tea party movement. Obama said mandated coverage also would justify requiring insurers to cover people with pre-existing medical problems because Americans would be unable to wait until they were seriously ill or injured – and therefore expensive to treat – before seeking insurance.

Obama, his allies and some independent analysts say Romney’s state programme was a model for the federal law. Romney rejects the claim. He says his programme was less costly and intrusive and was designed for one particular state, not the entire nation.

Mandated coverage is at the heart of the constitutional question, however. That complicates Romney’s efforts to distance himself from what he calls ‘Obamacare’.

It’s impossible to predict with confidence how the high court will rule and how the eventual ruling, whatever it is, will affect the 6 November elections.

If the healthcare law is ruled constitutional, it presumably will give Obama and congressional Democrats a boost. That’s especially true if a high-profile conservative justice such as Antonin Scalia or Chief Justice John Roberts votes to uphold it. That would undercut conservative activists’ efforts to portray the law as a partisan product of liberal Democrats.

A pro-Obama ruling, however, might intensify conservative voters’ efforts to give Republicans control of the House of Representatives, Senate and White House this fall, in hopes of rewriting the nation’s health laws.

Some liberals say the biggest problem has been Democrats’ failed efforts to convince most Americans that the 2010 law is good for them. Provisions already in place, such as letting young adults stay on their parents’ employer-provided health plans and barring insurance companies from denying coverage to minors with pre-existing conditions, have not triggered the public enthusiasm that Obama’s allies predicted two years ago.

Heavy coverage of the Supreme Court case “gives us a chance to explain the law to Americans who are sceptical about it because they don’t understand it,” said Vincent DeMarco, president of the Maryland Citizens’ Health Initiative and one of many activists standing outside the court building this week.

“They think it’s a single-payer system, which it’s not,” DeMarco said. People also don’t realise that requiring everyone to have insurance, including healthy people who seek few medical services, will lower costs for others and force insurers to stop discriminating against those with pre-existing conditions, he said.

If the Supreme Court strikes down the 2010 health law, some conservatives fear it will depress Republican turnout in the November election because opponents no longer can argue that ousting Obama is the only way to kill ‘Obamacare’.

Some conservative activists who demonstrated outside the court this week played down the potential impact on the presidential race regardless of how the court rules. Rejection of the law would chiefly raise questions about a Democratic-controlled Congress that passed such a flawed bill, said Jenny Beth Martin of Atlanta, co-founder of Tea Party Patriots.

Jim Manley, a former Democratic Senate aide, said Romney’s likely nomination will negate the issue’s impact in the presidential race.

“If the Supreme Court overturns this, the politics will take care of itself in November,” Manley said. “But I guarantee Mitt Romney is not going to get any political gain out of this. He’s tied at the hip” to the individual mandate being weighed by the high court.

Charles Babington covers politics for The Associated Press. Associated Press writers Laurie Kellman and Henry C. Jackson contributed to this report.