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President Barack Obama announced Wednesday that the U.S. and Cuba have struck a deal to open embassies in each other's capitals and re-establish diplomatic relations for the first time in half a century.

"The progress we make today is another demonstration we don't have to be imprisoned by the past," Obama said.

Obama emphasized that the U.S. and Cuba have some shared interests, such as strong anti-terrorism policies and disaster response. But he acknowledged that the two nations still have "very serious differences" on issues like free speech.

"We won't hesitate to speak out when we see contradiction to those values," the president said.

According to a statement from the Cuban government, officials are aiming to reopen their embassy on or after July 20. White House deputy national security adviser Ben Rhodes told MSNBC that the U.S. will open its embassy in Cuba "shortly after" July 20.

"In making this decision, Cuba is encouraged by the reciprocal intention to develop respectful and cooperative relations between our two peoples and governments," Cuban President Raúl Castro wrote Obama in a letter.

Obama wrote Castro that both nations are making "an important step" toward normalizing relations.

Related: U.S., Cuba to Announce Deal to Open Foreign Embassies

Obama announced in December that the U.S. was ending an "outdated approach" of isolating Cuba, and in May the U.S. dropped Cuba from its list of state sponsors of terrorism.

This formal step follows Obama's call to normalize relations and economic ties between the two countries after decades of Cold War hostilities. The U.S. severed diplomatic relations with the communist island country in 1961.

Secretary of State John Kerry. who announced Wednesday that he will travel to Cuba later in the summer, called the resumption of diplomatic relations an "important step" in comments that followed the president's remarks.

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Some Cuban Americans greeted the news with cautious optimism.

Adam San Miguel, 30, who was born and raised in Hudson County, New Jersey, to parents who fled Cuba, called the historic announcement "bittersweet."

"While we recognize this is a positive change for the people of Cuba, there's an aspect of dancing with the devil," said San Miguel, the director of a network of New York -area Cuban Americans. Another resident and activist was more hopeful, saying "change won't happen overnight, but the Castros aren't going to be in power forever."

Related: Hope, Skepticism As U.S., Cuba Agree to Open Embassies

The move to normalize relations follows a historic meeting between Obama and Castro in Panama at the Summit of the Americas earlier this year. Just before that meeting, the State Department recommended to Obama that Cuba be taken off the list.

It's also another major development in the U.S. relationship with Cuba since the president announced plans in December to restore full relations with Cuba and high-level talks began to open an embassy in Havana. The evolving shift away from Cold War policies that governed the U.S.-Cuba relationship has led to other changes that could be accomplished without approval from Congress.

However, there's no indication the Republican majority in Congress is interested in codifying the normalization of relations with Cuba.

The Republican majority in the House and the Senate is not interested in funding a new embassy — although it appears that is not needed — or to approve an ambassador or lifting the trade embargo that has been in place since the 1960s.

Relations with the Castro regime should not be revisited until the Cuban people enjoy freedom: http://t.co/LSItCiEX9t #Cuba — Speaker John Boehner (@SpeakerBoehner) July 1, 2015

The two congressional leads on any moves in the Senate regarding the Cuba-U.S. relationship would be Senate Foreign Relations Chairman Bob Corker, R-Tennessee, and Sen. Marco Rubio, R-Florida, who is Cuban American and a GOP presidential hopeful.

Related: U.S.-Cuba Relations: From Obama to Castro, Who Are the Key Players?

"Throughout this entire negotiation, as the Castro regime has stepped up its repression of the Cuban people, the Obama administration has continued to look the other way and offer concession after concession," Rubio said in a statement. "The administration's reported plan to restore diplomatic relations is one such prized concession to the Castro regime."

Rubio said he intends to oppose confirmation of an ambassador to Cuba until there is a resolution on such issues as "the return of U.S. fugitives being harbored in Cuba, settling outstanding legal claims to U.S. citizens for properties confiscated by the regime, and in obtaining the unequivocal right of our diplomats to travel freely throughout Cuba and meet with any dissidents, and most importantly, securing greater political freedoms for the Cuban people."

Related: Obama Nixing Cuba From List of State Sponsors of Terrorism

But House Democratic leader Nancy Pelosi applauded the announcement.

"Reopening embassies lays the foundation for a new, more productive relationship with Cuba that can support and advance key American priorities — including human rights, counter-narcotics cooperation, business opportunities for American companies, migration, family unification, and cultural and faith-based exchanges," Pelosi said in a statement.

However, her Republican counterpart, Speaker John Boehner, echoed the sentiments of many in his caucus who have expressed concerns about the administration's efforts.

"The Obama administration is handing the Castros a lifetime dream of legitimacy without getting a thing for the Cuban people being oppressed by this brutal communist dictatorship," Boehner said in a statement. "As I've said before, relations with the Castro regime should not be revisited, let alone normalized, until Cubans enjoy freedom — and not one second sooner."

The president acknowledged that there would be congressional opposition. He urged lawmakers not to "double down on a policy of isolation."

"Americans and Cubans alike are ready to move forward. I believe it's time for Congress to do the same. I've called on Congress to take steps to lift the embargo that prevents Americans from traveling or doing business in Cuba," Obama said Wednesday. "We've already seen members from both parties begin that work. After all, why should Washington stand in the way of our own people?"