Barack Obama, Hillary Clinton and John McCain are agreed on one thing.

They are all worried about Ted Kennedy.

While cynicism is always appropriate when dealing with politicians, this concern is genuine.

Anyone who knows anything about the U.S. Senate knows why there is complete unity when it comes to hoping that Ted Kennedy will come through his current medical scare rested and ready to continue serving.

Since 1980, when he surrendered his presidential ambitions, Kennedy has devoted himself to the Senate. Even when Republicans ran the chamber, he was considered the essential player — so much so that George W. Bush and Dick Cheney courted him. Despite all the pokes he took from right-wing interest groups and media, conservative Republicans have known the liberal lion as a man of the Senate who forges the compromises — on judicial appointments, education and labor policy and just about everything else — that end up having staying power.

So everyone in the Senate, Democrats and Republicans, liberals and conservatives, gasped when the word came that Kennedy had suffered a seizure Saturday morning — perhaps two seizures, depending on the report — and was hospitalized in Boston.

The 76-year-old Kennedy, who came to the Senate in 1962, has had his share of hospitalizations and treatments in recent years — including surgery last October to address a partially blocked neck artery that doctors feared put him at risk of a stroke.

There’s no word yet on the precise nature of Saturday’s seizure. The 76-year-old senator’s office released a written statement just after 2 p.m. EST, but it merely acknowledged that, “It appears that Senator Kennedy experienced a seizure this morning. He is undergoing a battery of tests at Massachusetts General Hospital to determine the cause of the seizure. Senator Kennedy is resting comfortably, and it is unlikely we will know anything more for the next 48 hours.”

By Sunday, there were positive signals from doctors and the senator’s friends — who suggested that Kennedy was alert and engaged. But heremained in serious condition as more tests were done to determine what was wrong.

While the diagnosis was unclear, there was great clarity — and consistency — in the response from those who have worked most closely with the senior senator.

The news of Kennedy’s illness brought a rare show of unity from the feuding camps of Democratic presidential candidates Obama and Clinton and Republican McCain.

Said Obama, whose campaign won Kennedy’s endorsement and active support this year, “We are going to be rooting for him and I insist on being optimistic about how it’s going to turn out.”

Clinton, who was welcomed to the Senate in 2001 by Kennedy and regularly counseled by him, said she was praying for “a quick recovery.”

McCain, who has actually worked most closely with Kennedy in the Senate (especially on immigration issues, but also on a host of other matters), released the most detailed and laudatory statement.

“I was very sorry to hear that Senator Kennedy has taken ill, and like millions of Americans, Cindy and I anxiously await word of his condition. Senator Kennedy’s role in the U.S. Senate cannot be overstated,” said the presumptive Republican nominee. “He is a legendary lawmaker, and I have the highest respect for him. When we have worked together, he has been a skillful, fair and generous partner. I consider it a great privilege to call him my friend. Cindy and I are praying for our friend, his wife, Vicki and the Kennedy family.”