Sen. Marco Rubio talks to reporters on Tuesday. (Chip Somodevilla/Getty Images)

Sen. Marco Rubio has emerged as one of the loudest Republican critics of President Trump’s policies on China, the latest in a series of splits with party leadership by the Florida lawmaker, who might eventually run for president again.

For the fourth day in a row, Rubio took to Twitter on Wednesday to argue that China was besting the Trump administration in critical negotiations. He has used an assortment of hashtags to take aim at a developing deal to free a Chinese telecommunications firm from punitive action. Some, such as “#NotWinning,” play off the president’s signature catchphrases.

During Trump’s presidency, Rubio has strayed from party leaders a few times, including on gun laws, taxes and Trump’s first pick for secretary of state. But he has backed down from many of those challenges and fallen in line, raising questions about where his latest show of defiance will lead.

Like other ambitious Republicans in the Trump era, Rubio is looking for a way to craft his own, distinct image and sphere of influence in the party. Friends and associates say they believe the 46-year-old Rubio might wage a second presidential bid.

In taking on Trump over China, Rubio is speaking out on an issue he has talked about for years, including as a White House hopeful in 2016. Rubio has warned that China presents a national security threat to the United States.

This week, Rubio has voiced increasing alarm about the administration’s direction on China. Trump has been moving closer in recent days to freeing the embattled Chinese telecommunications company ZTE Corp. from severe penalties over export law violations, telling reporters that existing restrictions have harmed U.S. firms that sell material to China.

“#DoNotCave,” Rubio tweeted Wednesday. “I don’t understand how they can push for a deal that lets them keep operating in U.S.,” he added.

The Florida senator has long tried to distinguish himself from other Republicans on the basis of his foreign policy and national security expertise. A member of the Senate Foreign Relations Committee, Rubio has embraced traditionally hawkish GOP views on China, Russia and the position of the United States on the world stage.

He also witnessed firsthand in the 2016 presidential campaign the power of a protectionist trade message, on which Trump ran successfully.

Rubio tweeted Tuesday that China was “out-negotiating the administration & winning the trade talks right now.” He added: “This is #NotWinning.”

On Monday, Rubio wrote that China “is winning the negotiations,” using the hashtag “#Losing.” He’s warned that releasing restrictions on the Chinese firm, which is partly owned by the government, could put U.S. national security and intellectual property at risk.

Rubio’s allies say the tweets enable him to potentially grab Trump’s attention.

“That’s how you get things done with this administration. When Marco tweets, Fox picks it up, and that’s how the president sees it,” said one informal adviser to Rubio, who spoke on the condition of anonymity to be more candid.

But a Republican consultant close to the White House called the tweets “shortsighted.”

“What does Rubio get out of it? It will definitely get Trump’s attention, and Trump will choose to smack him down. What’s Rubio’s endgame?” asked the consultant, who also spoke on the condition of anonymity to openly share an assessment.

The White House did not respond to a request for comment on Rubio.

Rebutting the criticism that he was being too soft on China, Trump said Tuesday, “For those who say maybe Trump is getting a little bit easy — ZTE, we closed it.”

Rubio is far from the only lawmaker who has been issuing rebukes or caution on China and ZTE. But the Florida senator has been one of the sharpest critics.

“In the case of ZTE, I believe it’s not so much a trade or economic issue as it is a national security issue,” said Sen. Roy Blunt (R-Mo.), vice chairman of the Senate Republican Conference, offering a more measured take than Rubio has this week, but making the same general argument that the Floridian offered earlier this month. “And I’m sure we’ll continue to have conversations about that.”

Where Rubio goes from here is not completely clear. He said Tuesday he plans to “begin working on veto-proof congressional action.” In the past, Rubio has moved back from a contentious position after first leaning in.

Following the deadly school shooting in Parkland, Fla., in February, Rubio endorsed raising the age requirement for buying a rifle and said he was “reconsidering” his opposition to placing new limits on high-capacity ammunition magazines. But three months later, he has yet to embrace specific legislation on those two issues, which are unpopular with the powerful gun-rights movement that has dominated the Republican Party.

Last year, after voicing concerns about Rex Tillerson’s views on Russia after Trump nominated him as secretary of state, Rubio ultimately voted to confirm him.

And in 2013, Rubio was part of a bipartisan “Gang of Eight” senators who crafted a sweeping rewrite of the nation’s immigration laws that included a path to citizenship for undocumented immigrants. Later, he disavowed the plan, which came under heavy criticism from conservatives.

Rubio voted for the GOP tax law last year. But some Republicans believe he complicated the party’s vigorous defense of the measure with recent comments to the Economist magazine about corporations.

The senator’s advisers said that where he agrees with Trump, he will have no reservations about saying so, and when he disagrees, he will also speak out.

The Florida senator has found ways to work with Trump on foreign policy, including on his harder-line Cuba policy that marked a shift from the Obama administration’s approach. Rubio has also praised officials who are working with Trump to shape policies abroad, including Secretary of State Mike Pompeo and Treasury Secretary Steve Mnuchin.

But he is also trying to fashion his own brand, which took a significant hit in the 2016 presidential primary. Trump labeled him “Little Marco” to devastating effect. Rubio ended his campaign in his home state after Trump defeated him there by a wide margin.

As he plots his next steps, Rubio recently hired Mike Needham to be his chief of staff. Needham used to be the chief executive of Heritage Action for America, a conservative organization.

Even as he overhauls his team, there are still shades of his 2016 campaign theme — “A New American Century” — in his current rhetoric.

“Relationship between U.S. & #China will define 21st century,” he tweeted Wednesday.

Damian Paletta and David J. Lynch contributed to this report.