For both cadres, there is an evil lurking everywhere: compromise.

It’s a synonym for weakness and a reason to batter and berate an opponent, whether in your party or another.

Democrats are riding a tiger, as a friend put it, and best not be naïve about positive aspects of the Tea Party victories. The Democrats seem weak, unfocused, struggling with money and up against a Republican opponent with increasing amounts of cash and a simpler, though simplistic, message.

And now comes a voice from the grave — that of Everett M. Dirksen, Republican of Illinois, who was in Congress for 36 years, the last 10 as Senate minority leader — with a lesson for all.

His once famously hoarse baritone can be heard in a just-released tape of a conversation from Sept. 9, 1963, among President John F. Kennedy, Dirksen and Senator Mike Mansfield, the majority leader from Montana.

The secretly taped chat, which most likely took place in the Oval Office, was declassified recently by the John F. Kennedy Presidential Library and Museum in Boston and attracted no news media interest beyond an online tale in USA Today. That’s too bad.

The subject at hand was a big deal, namely debate in the Senate on whether to ratify the Limited Test Ban Treaty, or Nuclear Test Ban Treaty, basically barring all nuclear test detonations except those done underground. It had been signed in Moscow a few weeks earlier by the United States, the Soviet Union and Britain.

Given the cold war, Kennedy had to allay the qualms of many senators to secure a two-thirds vote of approval, even though his party controlled the chamber by 66 to 34.

That inspired the 33-minute chat dominated by Dirksen and including a late cameo appearance by Secretary of Defense Robert S. McNamara.

Dirksen spoke of the “overriding fear” of two key conservative Southern Democrats, Senators John Stennis of Mississippi and Richard B. Russell of Georgia. “The question is how you overcome it,” he said, adding that their anxiety turned on “whether we’d be disadvantaged by the Soviets.”

He proposed that Kennedy send a letter of reassurance to the Senate. “I hope you don’t mind that this is a little presumptuous on my part,” a deferential Dirksen said, proceeding to read aloud a copy he had already drafted.

It said that underground testing would be pursued without delay, that our detection facilities would be expanded and that we would support a “dynamic program of weapons development” and pursue nuclear explosives for peaceful purposes under the treaty’s rules.

Dirksen, a Republican, then counseled Kennedy, a Democrat, on how to mollify specific colleagues of both parties, as well as former President Dwight D. Eisenhower. To that end, he included a passage about using “every weapon at our command, including our entire arsenal of nuclear weapons” if any aggressor threatened our national interests.

Dirksen conceded that he had taken heat for his support of the treaty, for which The Chicago Tribune “excoriates me.” Kennedy joked that such barbs did not compare with those in a new book — “J.F.K.: The Man and the Myth” — by the conservative columnist Victor Lasky.

The president was clearly grateful for Dirksen’s counsel, underscoring that without such a treaty lots of countries, including Israel and Egypt, would seek a nuclear option. “We’d have a bitch of a situation,” he said.

Kennedy did send a letter to the Senate, and the treaty was ratified.

Now, can you imagine Mitch McConnell, the Senate minority leader and a Republican from Kentucky, lifting a finger to similarly assist President Obama?

I should have sent a transcript of the conversation to the crowd of Tea Party advocates who were set to cheer Glenn Beck on Saturday at Sears Centre in Hoffman Estates.

Imagine the hissing. Such compromise would be seen as treason.

For the moment, party power, even to do nothing, is more important than the national interest.