U.S. politicians off and on the campaign trail made it known there was no love lost for Cuban leader Fidel Castro after his announcement Tuesday that he would step down as ruler of the communist regime.

President Bush expressed hope that the change would launch a transition to democracy in Cuba after nearly 50 years of hardline, communist rule.

"What does this mean for the people in Cuba?" Bush said at a news conference during his trip to Africa. "They're the ones who suffered under Fidel Castro. They're the ones who were put in prison because of their beliefs. They're the ones who have been denied their right to live in a free society. So I view this as a period of transition and it should be the beginning of the democratic transition in Cuba."

Click here to read quotes from other U.S. officials on the resignation of Fidel Castro.

Presidential candidates Barack Obama, Hillary Clinton and John McCain called for the release of political prisoners in Cuba.

Castro's resignation "should mark the end of a dark era in Cuba's history. ... Fidel Castro's stepping down is an essential first step, but it is sadly insufficient in bringing freedom to Cuba," Sen. Obama, D-Ill., said in a statement.

"Cuba's future should be determined by the Cuban people and not by an anti-democratic successor regime," Obama said. "The prompt release of all prisoners of conscience wrongly jailed for standing up for the basic freedoms too long denied to the Cuban people would mark an important break with the past. It's time for these heroes to be released."

Obama also urged that the United State be prepared to take steps to normalize relations with Cuba and to ease the trade embargo of the last five decades if the Cuban leadership "begins opening Cuba to meaningful democratic change."

Sen. McCain, R-Ariz., also underscored that "freedom for the Cuban people is not yet at hand" despite Castro's resignation.

"We must press the Cuban regime to release all political prisoners unconditionally, to legalize all political parties, labor unions and free media, and to schedule internationally monitored elections," McCain said in a statement.

"Cuba's transition to democracy is inevitable; it is a matter of when not if. With the resignation of Fidel Castro, the Cuban people have an opportunity to move forward and continue pushing for the moment that they will truly be free. America can and should help hasten the sparking of freedom in Cuba. The Cuban people have waited long enough."

Speaking at a campaign stop in Ohio, Sen. Clinton, D-N.Y., said, "I think this provides a great opportunity for the people of Cuba. I’m hoping the next leadership will take steps to move Cuba toward democracy, release prisoners, lift burdens that have prevented the Cuban people from having the kind of future they deserve to have."

Clinton said she believed the United States would meet with a new Cuban government "if they demonstrate they’re willing to change. ... But it is a very stark reminder that even if you’ve been in power for 50 years, you cannot hold on to power forever."

Former Arkansas Gov. Mike Huckabee, also a GOP White House hopeful, said, "The Cuban people deserve nothing less than free and fair elections which would provide the only hope for a prosperous and democratic Cuba. Until Fidel Castro is dead there can be no significant movement towards reform in Cuba.

"Raul Castro has proven that he's as much a tyrant and dictator as his brother Fidel. Simply providing more power to another dictator does nothing to promote freedom and democracy to the Cuban people." Both Republican and Democratic Senate leaders said the focus now should be on bringing political freedom to the Cuban people.

"Today's news from Cuba should not focus on one man who is merely formalizing the transfer of power he initiated a year and a half ago," Senate Majority Leader Harry Reid said. "It should focus on the more than 11 million Cubans who still seek the freedom they deserve. After nearly 50 years of an oppressive regime, it is long past time for democracy to displace dictatorship, and we must continue to support those who long for liberty in Cuba."

And Senate Minority Leader Mitch McConnell criticized Castro's heir apparent, brother Raul Castro

"Let us hope that the long ruthless dictatorship of Fidel Castro is truly over, and that freedom and democracy may come to Cuba. Replacing one dictator with another, as appears to be the case, isn't the answer to the repression, brutality and fear produced by five decades of Castro," McConnell said.

He continued: "But that doesn't diminish the hope for or the efforts toward the day when the Cuban people can choose their own leaders and enjoy the freedom that Castro so relentlessly denied."

Rep. Ileana Ros-Lehtinen, a Miami-area Republican who was born in Havana, called for Castro's indictment and said his resignation was irrelevant because his regime had already "done great harm to the suffering Cuban people."

"It matters nothing at all whether Fidel, Raul or any other thug is named head of anything in Cuba," she said. "What the people want is freedom to vote in multiparty elections that are internationally supervised and freedom to express their dissent from the oppressive regime. The Communist machinery is enslaving them so it doesn't matter who the thug of the moment will be."

She then called on the Justice and State departments to indict Casto in connection to 1996 the deaths of three U.S. citizens and a U.S. resident, Carlos Acosta, Armando Alejandre, Mario de la Peña and Pablo Morales, when they were shot down by Cuban fighter jets.

"This is but the first step in bringing Fidel and other Cuban war criminals to justice," she said.

Castro's History of Anti-Americanism

It wasn't the Bay of Pigs invasion or the U.S. embargo against Cuba that turned Castro against the United States. He was in the anti-American camp long beforehand.

He never wavered in his loathing of his powerful neighbor to the north.

His feelings were dramatized in a handwritten note he sent to a colleague in 1958, as a guerrilla commander, six months before taking power.

"I am going to launch another, much longer and bigger war against them (the Americans). I realize now that this is going to be my true destiny," Castro, then 31, wrote.

He kept his word. His differences with the United States were more than just political; they were cultural as well. He ridiculed American elections, American consumerism, the American penchant for changing cars every few years and the perceived American indifference to society's less fortunate

Castro has contended that American domination of Cuba during the last century was such that the island did not achieve genuine independence until his revolution in 1959. He once denounced American imperialism 88 times in a single speech. His government confiscated, without compensation, almost 6,000 properties belonging to Americans.

Cuba under Castro had a 30-year partnership with the Soviet Union. When it came to Moscow's worldwide quest to pick up new allies for the socialist camp, no country was a more faithful supporter than Cuba. Castro also struck up friendships with other bitter enemies of the U.S.: North Korea, Iran and Iraq under Saddam Hussein — all members of Bush's "axis of evil."

Castro dreamed of Cuban-style communist revolutions throughout the Third World and was displeased about the global trend toward the embrace of free markets and representative democracy.

But he welcomed the emergence in recent years of left and center-left governments in Latin America, most notably in Venezuela, whose petrodollars, mostly from the United States, finance Venezuela's anti-American policies.

A major sore point for Cuba was the frequency with which anti-Castro militants launched attacks on Cuba, using Florida as a staging area.

During the early years of his rule, American missteps played into Castro's hands. The botched Bay of Pigs invasion of 1961 made him the country's unquestioned leader and sullied the American image around the world. Later, that image was further damaged by disclosures of repeated CIA attempts in the early 1960s to assassinate Castro.

Between 1959 and 1962, Castro had an enormous impact on American policy toward Latin America. Fearful of a wave of Castro-type revolutions in the hemisphere, President Kennedy promoted a dramatic expansion of U.S. assistance to — and involvement in — Latin America.

It was only after the Cuban missile crisis in 1962 — in which Castro was essentially a bystander — that U.S. concerns about Castro's influence in the region began to ebb.

The centerpiece of American policy toward Cuba has been the economic embargo, first instituted in limited form in 1960 and strengthened in 1962.

Castro persistently called the embargo "criminal," and claimed that its economic impact on the island ran well into the tens of billions of dollars. Politically influential anti-Castro militants have beaten efforts over the years to lift the embargo.

Internationally, the embargo has virtually no support. Each fall, the U.N. General Assembly takes up a Cuban-sponsored proposal to condemn the measure. Normally, the United States can count on few votes beyond its own.

Migration issues have repeatedly roiled the U.S.-Cuban relationship. In 1980, 125,000 Cuban boat people fled to South Florida. Castro outraged many Americans by allowing criminals and the mentally ill to join the exodus.

The last president to make a serious effort to establish normal relations with Cuba was Jimmy Carter; he gave up the effort after less than a year. The two countries have not had discussions on political issues since 1982.

With the collapse of the Soviet Union in 1991, the focus of Washington's complaints has shifted from Cold War concerns to the absence of freedom in Cuba and its treatment of dissidents.

When Cuban authorities arrested 75 regime opponents and sentenced them to lengthy prison terms in March of 2003, the Bush administration's response was predictably harsh. Cuba accused the dissidents of engaging in subversive activities at U.S. behest.

Washington insists that there can be no normal relations until Cuba releases political prisoners and takes credible steps toward establishing democratic rule.

Bush said in May 2002: "The goal of the United States policy toward Cuba is not a permanent embargo on Cuba's economy. The goal is freedom for Cuba's people."

On Tuesday from Africa, Bush struck up the same theme, noting that he had met with the families of some of prisoners, and that their release should be the first step of any transition to democracy. "It just breaks your heart to realize that people have been thrown in prisons because they dare speak out," he said.

Castro has expressed belief that his revolution will survive him. The administration sees the Cuban people as starved for freedom and is trying to hasten a transition to democracy. It has been assisting non-governmental groups in Cuba to achieve that goal. To reduce Castro's access to dollars, it has sharply restricted travel by Americans to Cuba.

Only rarely during Castro's rule did the United States and Cuba find common ground. One such occasion was the Elian Gonzalez affair in 1999-2000.

When the Clinton administration allowed the shipwreck survivor, age 7, to be returned to Cuba over the objection of Cuban-American relatives in South Florida, Castro expressed gratitude to the Clinton administration — but made clear his appreciation was only temporary.

"Tomorrow the struggle continues," Castro said.

The Associated Press contributed to this report.