The federal health-insurance law, dubbed by both sides as "Obamacare," already has become the top issue in Missouri’s U.S. Senate contest – a fact that only heightens the impact of this week’s hearings in Washington before the U.S. Supreme Court.

U.S. Sen. Claire McCaskill, D-Mo., acknowledged as much on Sunday, as she defended the federal Affordable Care Act while also pledging to defend military veterans’ health benefits from the cuts that she asserts are included in the Republican budget plan before the U.S. House.

Meanwhile, the Republicans competing for a chance to challenge her this fall have all condemned the health-care changes – while also battling over who’s been the toughest to oppose Medicare’s existing prescription drug benefit.

St. Louis businessman John Brunner and former state Treasurer Sarah Steelman both have maintained in recent debates that they would have voted against the drug benefit when it was enacted in 2006. Both have accused the third GOP Senate hopeful, U.S. Rep. Todd Akin, R-Wildwood, of backing the benefit because he initially voted for it before casting a final vote against it. (Akin says the final version had changes he couldn't support.)

The three also have repeatedly attacked McCaskill over her 2010 vote for the health-care reform. Her vote also has figured in a number of attack ads already running in Missouri; the ads were produced and paid for by independent political-action committees known as "Super PACs."

UPDATE: Brunner issued a statement today underscoring his hope that the Supreme Court would toss out the Affordable Care Act, particularly its mandate that most Americans purchase health insurance.  "If the Supreme Court somehow fails to overturn this unconstitutional mandate, the next Congress must fight to repeal ObamaCare," Brunner said. "But, in order to pursue a legislative repeal, politicians who supported ObamaCare like Claire McCaskill must be defeated this November." end update

U.S. Sen. Roy Blunt, R-Mo., also laid out his opposition to "Obamacare" in an op-ed over the weekend in the Springfield, Mo. News-Leader.

McCaskill listened to fears about possible cuts in veterans health and disability benefits – or rumored new taxes on them -- during a forum Sunday with area veterans held at the Soldiers Memorial downtown.

She told the veterans that she and other Democrats controlling the Senate would block the budget proposed by U.S. House Budget chairman Paul Ryan, R-Wisc., which she said would have to slash veterans benefits – or tax them -- significantly to meet the fiscal targets Ryan is proposing.

The senator emphasized that Ryan's budget plan also would reduce the tax rate for businesses and cut the rates for the wealthy.

McCaskill explained later that the Ryan budget calls for a 33 percent cut in mandatory domestic spending, which she said would have to affect veterans programs because they constitute about one-third of such federal spending.

“I think they are trying to pull the wool over veterans’ eyes,’’ she said.

McCaskill contended that the same Republican approach is at work in their criticisms of the federal health-care law. She told reporters that the law will gain more public support as more provisions go into effect – if, she added, those provisions are allowed to go into effect.

“There’s a lot of good in the bill that people are not aware of,’’ she said, while acknowledging that Republicans and their allies have done a better job of attacking the program than Democrats have done in defending it.

She pointed out that she’s now a target of a TV attack ad that features entertainer Pat Boone, who contends in the spot that McCaskill is out to cut Medicare. The ad is a “cookie-cutter’’ spot, meaning that identical versions – but attacking different Democrats –have been running in several states with hot U.S. Senate contests and vulnerable Democrats.

The ad was created by a conservative group called the 60-Plus Association.

McCaskill says the ad is inaccurate because it focuses on a provision in the federal law that ends extra payments to insurance companies for the Medicare "advantage" program. The Ryan budget, she said, includes the same cut.

McCaskill also emphasized that the latest Ryan budget proposal would, like his original one, transform Medicare largely into a voucher program in which the elderly would get a government subsidy to help them purchase private insurance; the elderly would have to cover any additional costs.  

She pointed out that her three GOP rivals have embraced Ryan’s proposal and that Akin has voted for it.

McCaskill said she also plans to highlight the Republican candidates’ opposition to the Medicare prescription drug benefit, although she didn’t offer any details. She said the benefit has helped many elderly who could not otherwise afford their prescriptions; McCaskill noted that the benefit is expanded in the federal health insurance changes known as "Obamacare" that the GOP also derides.

She did, however, quip to the veterans that they shouldn’t be surprised if Pat Boone is featured in a new attack ad that “claims McCaskill is killing vets.”