Sen. John McCain (Ariz.), the Republican Party’s presidential candidate, described Sen. Edward Kennedy (D-Mass.) on Tuesday as “the single most effective member of the Senate.”

It was perhaps a politically dangerous thing to say, given that Kennedy is viewed among many grassroots conservatives as an unmatched liberal bogeyman.

McCain needs conservatives’ votes in November, and has been doing much recently to allay their concerns that he is not really one of them; he has, for example, given them forceful reassurances that he would, as president, nominate conservative judges.

The candidate’s praise for Kennedy was not likely, therefore, to have been a gratuitous slap toward his base — the kind of thing for which he is known and not wholly trusted.

Rather, it was a testament to the affection and respect that Kennedy has earned during his 46 years in the Senate. That period of public service makes him the third longest serving senator in history, and in that time he has become an institution within that institution.

His political opponents and even his personal detractors acknowledge that the senior Massachusetts senator is an extraordinarily capable legislator. He has proved able repeatedly to craft and push through bipartisan bills co-authored or supported by lawmakers and presidents with whom he agrees on few, if any, other policy prescriptions. The No Child Left Behind Act of President Bush’s first term was a notable example of Kennedy’s skill.

Now the Senate has received the shocking news that Kennedy has been diagnosed with a malignant brain tumor. We hope that this diagnosis proves incorrect, just as a similar one did for Sen. Arlen Specter (R-Pa.). But whether the diagnosis is right or wrong, we wish Kennedy a full and speedy recovery.

That wish was universal among stunned senators when they heard the news of his life-threatening illness. Democrats close to Kennedy were profoundly subdued, and several shed tears for the man they have come to love.

But the GOP, too, was laid low by the news from Massachusetts because, as Sen. Lamar Alexander (R-Tenn.) noted, “Republicans have as much affection for Ted Kennedy as they do for any other member of the Senate.”

Kennedy’s ability to reach across the aisle has not been confined to the craft of legislating but also extended to the quality of friendship.

As many political foes would testify and as the senator would admit, Kennedy has conducted his career so as to retain and entrench his influence in the federal government — being as harshly belligerent as anyone in his politicking and rhetoric when it was advantageous to be so, but also being as ameliorative and supple as the next man when that was his means to a better return.

Being described as the “most effective” member of the Senate is a tribute with which most of Washington will agree. It is a tribute to a politician who has displayed the political passion, personal vigor, intellectual suppleness and negotiating steel required to get things done.