President Trump is taking aim at Senate Republican healthcare holdouts in the final hours before a key procedural vote, which has some inside the GOP saying Trump's aggressive move should have come sooner.

"They would be [moving Senate votes] if he started this at the beginning of the process," said Jim Dornan, a Republican strategist. "It's almost too little too late."

"The speech was great, if it had happened five months ago!" a Republican congressional aide said of Trump's White House remarks on Obamacare Monday.

Trump didn't exactly spare the Democrats any criticism. "They run out. They say, ‘Death, death, death," he said in his Monday appearance with families who say they have been hurt by the healthcare law. "Well, Obamacare is death. That's the one that's death."

"The problem is we have zero help from the Democrats. They're obstructionists — that's all they are," Trump said. "The Democrats aren't giving us one vote, so we need virtually every single vote from the Republicans. Not easy to do."

But it was clear that Republicans in the upper house of Congress were Trump's main target audience.

"For Senate Republicans, this is their chance to keep their promise," Trump said. "Over and over again, they said repeal and replace, repeal and replace. But they can now keep their promise to the American people."

Trump defined the stakes in stark terms.

"Any senator who votes against starting debate is telling America that you are fine with the Obamacare nightmare," he said. "The question for every senator, Democrat or Republican, is whether they will side with Obamacare's architects ... or with its forgotten victims."

During later remarks to the Boy Scouts in West Virginia, Trump joked about firing Secretary of Health and Human Services Tom Price, a former Republican member of Congress, if he couldn't whip enough votes to start debate on a healthcare bill in the Senate — including that of the state's GOP Sen. Shelley Moore Capito.

"He better get Sen. Capito to vote for it," Trump said. "Better get the other senators to vote for it, it's time."

"The Trump White House is throwing everything including the kitchen sink at the Senate Republicans to get this done," said Ford O'Connell, a Republican strategist. "Whether it is working or not is unclear, because we are talking about a couple of holdouts."

Yet some wonder why Trump didn't take to the campaign trail in friendly states to help pass a healthcare bill and noted that Obamacare might not have passed in the first place without former President Barack Obama applying similar pressure on recalcitrant Democrats.

While Trump's job approval ratings are stuck around 40 percent nationally, somewhat limiting his leverage, he remains popular in a number of states with wavering Republican senators.

Trump is at 60 percent approval in Capito's West Virginia, which he won by more than 40 points in November, according to Gallup. He is at 53 percent in Kentucky, where Sen. Rand Paul is still a "no" vote on the GOP bill. He's also at 53 percent in Kansas, where Sen. Jerry Moran nearly torpedoed repeal-and-replace efforts by joining Sen. Mike Lee, R-Utah, in opposition.

The president has a 51 percent approval rating in Louisiana, home of Sen. Bill Cassidy. He is also at 51 percent in Alaska, where Sen. Lisa Murkowski is holding out. In North Dakota, where Democratic Sen. Heidi Heitkamp is up for re-election next year, 59 percent approve of Trump's job performance.

In each of these states, Trump is even more popular among Republicans. So while he might merely be breaking even in job approval rating in Ohio, his numbers are likely strong with those who form the base of support for Sen. Rob Portman.

"I think he's a really smart guy," said Dornan, "but I don't understand why he doesn't use the very bully pulpit he won on to win on this."

Others suggest the problem lies on the other side of Pennsylvania Avenue.

"It's mind-boggling that the president even needs to remind Senate Republicans to keep their long-standing promises," said Erin Montgomery, communications director for the pro-Trump America First Policies. "This is what the voters elected their representatives to do: repeal and replace Obamacare."

"That being said, never underestimate President Trump's keen ability to persuade and negotiate to ensure the best possible solution for the American people," she added.

"The problem is the Senate holdouts [both moderates and conservatives] aren't seeing the larger picture and that is ‘something is better than nothing' and inaction is not an option given tax reform looming in the distance," said O'Connell. "Democrats won't take back the House or limit GOP Senate gains because of Trump's tweets or comments. Dems will make big electoral gains if congressional Republicans prove themselves inept at governing."

This is the second time in as many weeks as Trump has challenged Senate Republicans to keep their Obamacare promises. The president invited all GOP senators to the White House for a lunch meeting to revive healthcare talks last week, chiding them in front of the cameras.

The Senate is set to vote on a motion to proceed on healthcare legislation Tuesday.