Cuban dictator Raul Castro has been making public and private overtures to American adversaries over the last several weeks, particularly Russia, at the same time the U.S. was investigating how U.S. officials stationed in Cuba mysteriously fell ill.

The combined events could point to a backsliding in U.S.-Cuba relations that former President Barack Obama worked to hard to put on a more productive path in the last few months of his administration.

Some Republicans already see the harm done to American officials in Havana — reportedly a "sonic attack" that caused hearing loss — as a basis for walking away from Obama's plan. But the meetings with Russia could also soften support for normalization among Democrats, who have a renewed sense of the threat posed by Russia in light of the 2016 election interference.

Cuba has been quietly reaching out to Russia over the last few weeks. Castro's team has huddled twice with senior Russian officials since the last week of July.

Specifically, Castro's foreign ministry sent the "head of the United States division," Josefina Vidal, to Moscow for a meeting with deputy foreign minister Sergey Ryabkov in late July, the Russian Foreign Ministry announced. Ryabkov then met with the Cuban ambassador to Russia on Wednesday.

Few details of the meetings are available. Cuba's foreign ministry did not publish a summary of the discussions, while the Russians provided only the briefest of readouts.

"During the meeting, the officials noted the steady development of friendly relations between Russia and Cuba," the Russian foreign ministry said following the meeting with Cuba's expert on the United States. "The parties also exchanged views on current issues on the international agenda."

The summary of Ryabkov's second meeting with a Cuban official was similarly spare. "Current economic bilateral cooperation matters as well as plans for upcoming bilateral contacts were the subjects of discussion," the Russian diplomats said following the meeting with Ambassador Emilio Lozada Garcia.

Republican opponents of the Obama's Cuba policy regard the meetings as a new vindication of their view.

"Russia continues to try to expand its presence in the Western Hemisphere, and Cuba has been a key ally to Putin," Sen. Marco Rubio, R-Fla., told the Washington Examiner.

"This is yet another reason why President Obama's decision to enrich the Cuban military and share intelligence with the Castro regime was terrible policy and counter to the national security interests of the United States," he said.

Cuba has also made an effort to reach out to Venezuela. Castro sent a letter of support for Venezuelan President Nicolas Maduro's effort to rewrite his nation's constitution and strip power from opposition leaders. The Trump administration not only opposed those moves but imposed sanctions on Maduro and other Venezuelan officials as a result.

South American leaders have urged Castro to join an effort to pressure Maduro to abide by the constitution. But Castro endorsed Maduro's latest move to establish a new legislative body on the strength of a government-approved referendum, even though millions of Venezuelans voted against the change.

"The demonstration of popular support has been clear and resounding," Castro wrote in a letter to Maduro published Thursday. He also pledged "militant solidarity" with Venezuela's authoritarian leader, with a clear allusion to American-led sanctions and countermeasures.

"Surely, there will come days of intense struggle, of international harassment, of blockades, of limitations; but they will also be days of creation and work for revolutionaries and all the Venezuelan people who, as before, will not be alone and will have us Cubans, in the front line of militant solidarity and more committed to their cause," Castro wrote to Maduro on Thursday.

The alleged sonic attack against U.S. officials is complicating the picture further. The U.S. expelled two Cuban officials in response, but U.S. officials have been unable to explain exactly what happened.

"This is a situation that we're still assessing," State Department spokeswoman Heather Nauert told reporters Thursday. "When I say an active investigation is underway, in part what that means is we don't know exactly where this came from. We can't blame any one individual or a country at this point yet."

One source close to the issue said the State Department would brief House and Senate staffers next week about what they know about these "sonic attacks," which seem to have started while former President Barack Obama was still in office.

That is likely to lead Republicans in particular to push the State Department for answers about when the Obama administration knew what was going on and what, if anything, officials last year tried to do about it. That's a clear sign that Republicans will be looking for details about whether Obama tried to hide Cuba's questionable activities in order to help preserve the fragile relationship that already appears to be coming apart.

"The real story here is, what was the Obama administration doing?" one source told the Washington Examiner. When asked if Republicans would be pushing for those answers, the source said, "Hell yeah."