WASHINGTON -- U.S. President Donald Trump expressed his frustration with Republicans on Sunday, saying they "do very little to protect their President."

In one of several tweets issued in the afternoon and evening, Trump said the lack of support happens even with "some that were carried over the line on my back."

Trump's tweet wasn't clear about why he was upset. It came as Republicans in the Senate struggled to come together on a bill to overhaul President Barack Obama's health care law.

On that topic, another tweet from the president was more specific: "If Republicans don't Repeal and Replace the disastrous ObamaCare, the repercussions will be far greater than any of them understand!"

Senate Majority Leader Mitch McConnell was making a last-gasp effort to resuscitate the legislation after Trump insisted that senators not leave town for their August recess without passing a health bill.

Trump has had a complicated relationship with the Republican Party, but GOP lawmakers have continued to be generally supportive of the president, even as his approval ratings slip.

Democrats did not escape Trump's twitter rantings as he turned his attention for a moment to the ongoing investigation into Russia meddling in the presidential election. In another missive he wrote: "As the phoney Russian Witch Hunt continues, two groups are laughing at this excuse for a lost election taking hold, Democrats and Russians!"

The president also took a shot at favourite targets in the news media: "It's hard to read the Failing New York Times or the Amazon Washington Post because every story/opinion, even if should be positive, is bad!"