WASHINGTON — President Trump on Monday blocked Broadcom’s $117 billion bid for the chip maker Qualcomm, citing national security concerns and sending a clear signal that he was willing to take extraordinary measures to promote his administration’s increasingly protectionist stance.

In a presidential order, Mr. Trump said “credible evidence” had led him to believe that if Singapore-based Broadcom were to acquire control of Qualcomm, it “might take action that threatens to impair the national security of the United States.” The acquisition, if it had gone through, would have been the largest technology deal in history.

Mr. Trump’s decision to prohibit the blockbuster deal underscored the lengths that he is willing to go to shelter American companies from foreign competition. In recent weeks, the president has turned to an arsenal of tools — including tariffs and an obscure government review panel — to ward off foreign control in American industries and, in particular, thwart the rise of China.

The president has focused many of these actions on the technology industry. While the United States has long claimed an advantage in tech, it is now facing emboldened rivals in China, where the government has heavily invested in everything from semiconductors to wireless networks to artificial intelligence. Through its recent actions, the White House has revealed its view that the country’s national security is tied to its advancement of those technologies.