Mr Helms, a Republican from North Carolina and chairman of the Senate Foreign Relations Committee, received a hero's welcome from thousands of Cuban-Americans. He warned that Cuba would be a priority issue for the Republicans, including their front-running presidential candidate, Bob Dole, until Mr Castro's regime ends.
"Let this be the year Cubans say farewell to Fidel. I don't care whether Fidel leaves horizontally or vertically, but he's leaving," Mr Helms told the flag-waving exiles, to chants of "Je-sse, Je-sse" and "Libertad" (Liberty).
Although the rhetoric was hardly fresh, Mr Helms and the Cuban-American leaders have clearly launched a new offensive on Cuba to outflank the Democrats. President Bill Clinton supports the embargo against Cuba, although he has opposed a proposed new law put forward by Mr Helms to tighten it and punish foreign firms that trade with Mr Castro.
The proposed Helms-Burton Law, or Cuban Liberty and Democratic Solidarity Act, would block such firms from doing business in the US and threaten legal action against anyone "trafficking" in property confiscated by the Castro government. As the regime essentially took control of the whole island, that threatens all foreign investment in Cuba.
"Repeat after me, `Time to go, Cas-tro'," Mr Helms said. The exiles did. "Hasta-la bye bye bye, Fidel," he added, but that one puzzled them.
"There was a man called Neville Chamberlain who went to Munich to make a deal with the devil and returned saying `We can do business with him', " he continued.
"We can't do business with Castro. You can dress him up in a suit, make him take a bath and have him sip tea with French intellectuals, but that does not alter the fact that he is an evil, cruel, murderous, barbarous thug.
"I'm talking about Canada, England, all those who caved in, who do business with Castro. Where I come from, when you do business with a tyrant, you're dealing in blood money. Where I come from, my friends, that's surrender.
"You remind me of one of my heroes in history, this extraordinary man, Winston Churchill," Mr Helms told the exiles.
"With his hand held high in defiance, he told his countrymen: `There can be no peace without freedom.' He told his people: `Never give up, never, never, never'. "
The Cuban Americans, some waving placards referring to "this cancer Castro" or "the Cuban holocaust," yelled the words back at him: "Never, never, never."
Mr Helms predicted his proposed law would be passed soon. As for its opponents, including the European Union, he said: "Oh, they'll get used to it.
"They're upset, according to press reports. However, I visited recently with John Major and he didn't even mention it. I think [opposition] will blow over."
Asked whether he thought he could win over Mr Clinton, he replied: "I think I'll talk to Hillary and tell her to persuade him."
Mr Helms visited the Little Havana area of Miami and laid a wreath at the monument to Cuban exiles who died in the abortive Bay of Pigs invasion of 17 April 1961, two years after Mr Castro's revolution. Although backed by the CIA, the invasion never received the promised US air support and the exiles were wiped out.
Commenting on veiled threats that President Castro would allow a repeat of last year's mass exodus if the Helms-Burton Law were passed, Mr Helms told the exiles, to cheers: "That is a military threat. We should meet it with an absolute naval blockade of Cuba."
Meanwhile, US and Cuban negotiators resumed talks in New York on immigration issues under an agreement reached last September to end the exodus of about 30,000 boat people. Most are now held in the US military base at Guantanamo Bay, on the eastern tip of Cuba.