WASHINGTON—Opposing sides in the debate over President Obama’s signature health care law converged outside the US Supreme Court Thursday morning to await a ruling that will have far-reaching impacts on the American healthcare system.

Competing chants rang out under a clear sky that promised a hot summer day. “Strike it down!” one group chanted, while another group proclaimed: “We love Obamacare!”

The crowd of hundreds overtook the sidewalk in front of the steps of the country’s highest court, providing a circus atmosphere to what will certainly a momentous day in the debate over the landmark law.

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Arkady Faktorovich, a Tea Party director from the small farming community of Los Banos, Calif., joined the throngs. “I don’t want this Ivanacare system to be imposed on me by the government,” he said.

Drums banged as he spoke, with signs floating above a sea of heads. Crowds swelled into the morning.

Karen Higgins, a nurse at Boston Medical Center’s intensive care unit, took an early flight to join Washington area nurses to weigh in. “It was important for me to be here,” said Higgins, a co-president of National Nurses United.

“No matter what the justices do, it will open the door for more discussion in this country.”

The union has long advocated a single-payer system modeled after Medicare, the government-run health program for seniors.

Edward Kimmel, a Washington area attorney, held up a large sign bearing the face of Senator Edward Kennedy, who championed the Healy care law. “The Dream Shall Never Die,” his sign said.

He marched with the same sign on March 22, 2010, outside the Capitol when the landmark legislation was passed by the House.

“I worked hard to get Obamacare passed,” he said.

Nearby, Katelynd Mahoney, who considers herself a devout Roman Catholic, matched with other women opposed to the health care law.

“Keep your ovaries off my rosaries,” her sign said.