The US Senate will vote as soon as next week on a Democratic-led effort to prevent President Donald Trump from launching an attack on Cuba, Senate aides said on Friday, responding to the Republican’s threats to take military action against the island.

Democratic Senators Tim Kaine, Adam Schiff and Ruben Gallego introduced the Cuba War Powers Resolution last month. Under Senate rules, the Senate’s Republican leaders must allow it to come up for a vote.

“The president’s saber rattling toward Cuba makes clear where his sights are next,” Schiff said in a statement when the resolution was introduced.

Exact timing of the vote has not yet been announced, but aides said they expected it before May 1.

Under Trump, US forces have launched strikes on boats off Venezuela and gone into Caracas to seize President Nicolas Maduro, and, with Israel, waged war on Iran since February 28, all without authorisation from Congress.

Trump has since said “Cuba is next,” while touting US military action in Venezuela and Iran. He did not specify what he plans to do with the island nation, but has frequently said he believes its government is on the verge of collapse.

Democrats have tried, and failed repeatedly in both the Senate and House of Representatives to force Trump to stop military action and obtain lawmakers’ authorisation before launching military operations.

Trump’s fellow Republicans, who hold slim majority in both the Senate and House, have almost unanimously voted to block the resolutions that have come up to date and there has been no indication yet that any are shifting position.

Although the US Constitution says that Congress, not the president, can declare war, that restriction does not apply for short-term operations or to counter an immediate threat.

The White House says Trump’s actions are within his rights as commander-in-chief to protect the US by ordering limited military operations. Congressional Republicans accuse Democrats of filing the resolutions only to attack Trump.