Trump issued on Monday an order barring the proposed mega-acquisition, saying there is credible evidence such a deal "threatens to impair the national security of the United States", according to a White House statement.
In such a scenario, Broadcom - which now works under the laws of Singapore - would have been considered as an American company and thus its proposed Dollars 117 billion would have been considered outside the preview of a federal agency - Committee on Foreign Investment in the United States (CFIUS) that reviews foreign deal. It added that "given well-known US national security concerns about Huawei and other Chinese telecommunications companies, a shift to Chinese dominance in 5G would have substantial negative national security consequences for the U.S".
When the president comes to San Diego on Tuesday, an explanation of his decision is needed - not just by residents but by nations that see themselves as US allies.
Further, Donald Trump ordered that both Qualcomm and Broadcom must "immediately and permanently abandon the proposed takeover".
"This decision is based on the facts and national security sensitivities related to this particular transaction only and is not meant to make any other statement about Broadcom or its employees, including its thousands of hardworking and highly skilled United States employees", Mnuchin said.
Broadcom, which says it will go ahead with its pledge to relocate to the U.S. from Singapore, said it was disappointed that President Trump had issued what was effectively a blocking order but reluctantly accepted it.
In a statement, Broadcom said it "strongly disagrees" that the acquisition raises any national-security concerns.
The decision to block the Broadcom deal also came as the Trump administration has taken a much harder stance on trade, imposing stiff new tariffs on imported steel and aluminum.
In a letter, the CFIUS had confirmed the national security concerns.
While Broadcom pursues Qualcomm and Intel waits, Qualcomm has also put a cash offer on the table to acquire another chipmaker, Netherlands-based NXP Semiconductors.
The order quashing the Broadcom-Qualcomm deal is being met with a wide range of reactions.
Broadcom has been going through a process of moving its legal headquarters to the U.S.in an effort to distance itself from its Asian roots.