WASHINGTON (NYTIMES) - For companies with supply chains that snake around the globe, the crises have just kept coming: First the prolonged and painful US-China trade war, then a coronavirus pandemic that snarled shipments, stalled international travel and shut factory doors.

President Donald Trump and his advisers have seized on the disruptions to make a familiar case to manufacturers: Come back home.

"The global pandemic has proven once and for all that to be a strong nation, America must be a manufacturing nation," Mr Trump said at a Ford factory in Ypsilanti, Michigan, on May 21. "We're bringing it back."

Mr Trump has spent much of his presidency trying to cajole manufacturers to return to the United States, through both tough talk and policies like tariffs. His advisers have pointed to both the trade war and the pandemic as evidence that it is just too risky for multinational companies to rely on other countries, particularly China, to make their goods.

But those arguments have yet to result in a wave of factories returning to the US. Foreign direct investment into the US - which measures spending from internationally owned companies to start, expand or acquire American businesses - sank drastically last year, to its lowest recorded level since 2006.

Foreign-owned companies invested about half as much in the US in 2019 as they did in 2016, the year before Mr Trump took office. After increasing in the first two years of Mr Trump's presidency, the number of manufacturing jobs flatlined last year and fell sharply with the pandemic. As of June, there were nearly 300,000 fewer factory jobs in the US than there were when Trump was inaugurated.

For all the president's criticisms of global supply chains, the economic incentive to outsource still prevails. While his trade policy has made doing business abroad, particularly in China, more uncertain and costly, higher wages in the US and the lure of foreign markets mean that most global businesses are choosing to remain global. Most firms that shifted out of China to avoid the crossfire of the trade war moved to other low-cost countries, like Vietnam and Mexico. Other companies say China is a growth market they cannot afford to lose.

And while the pandemic has prompted a broader reassessment of the risks of global supply chains, it has also brought about the deepest economic contraction in generations, battering companies' finances and forcing them to cut back on workers. Executives are deeply uncertain what demand for their products will look like in the coming months and years - hardly the environment to encourage big investments in new American factories.

The furniture maker La-Z-Boy is one example. The company shifted its production out of China to Vietnam last year to bypass Trump's tariffs on US$360 billion worth of Chinese goods. But on a June 24 earnings call, Kurt Darrow, La-Z-Boy's chief executive, announced that the economic effects of the pandemic would force the company to make steep cuts to its workforce, including in the US.

"While we were pleased to have brought back some 6,000 furloughed workers, we made the decision to permanently close our Newton, Mississippi, La-Z-Boy branded manufacturing facility and reduce our global workforce by approximately 10 per cent," he said.

Under the pressure of the trade war, some multinational companies have opened new facilities in the US, including Williams Sonoma and Stanley Black & Decker. Taiwan Semiconductor Manufacturing Co announced in May that it would set up a facility in Arizona, pending funding. Makers of masks and protective gear, like Honeywell and 3M, are expanding domestic production during the pandemic.

Politicians in both parties are offering proposals to encourage more manufacturing in the US, such as more funding for industries like semiconductors and pharmaceutical production.

The Trump administration's newly created US International Development Finance Corp may offer tens of billions of dollars to help reshore manufacturing of protective equipment and generic drugs. The administration is also considering other tax incentives and "reshoring subsidies," potentially as part of the next stimulus package, to try to lure factories home.

But there is little data to support claims by administration officials that their trade and tax policies have already encouraged significant reshoring of manufacturing or created a "blue-collar boom."

US factory output declined throughout 2019, as Mr Trump's trade war intensified, and it has dropped further this year, suggesting there is no boom in new American factories. Since peaking in mid-2019, corporate investment has declined for three consecutive quarters. Total foreign direct investment in manufacturing was nearly one-third lower in the first three years of Trump's tenure than it was in the final three years of President Barack Obama's.

Mr Trump ostensibly fought his trade war on behalf of American manufacturing. But economists say it has actually been a drag on most US factories, by increasing prices for components and inciting foreign retaliation. It has also coincided with a plunge in Chinese investment in the US to US$5 billion (S$6.9 billion) in 2019, the lowest level since 2009, according to Rhodium Group, a research firm.

Some Mr Trump officials and their supporters blame a broader global economic malaise that has dragged down factories worldwide. They point to the fact that imports fell last year and now account for a slightly smaller share of the goods consumed by Americans, as a sign of their success.

There are good reasons for some companies to leave China. Wages are rising, whittling away at one incentive to manufacture there. And deep fissures between the United States and China have opened in areas like security and technology, which could lead to more aggressive action by either side, regardless of who wins the presidential race in November.

Still, more companies leaving China does not necessarily mean a win for US workers. Like La-Z-Boy, many companies that are moving some facilities out of China - including Samsung, Hasbro, Apple, Nintendo and GoPro - are relocating to countries with even lower wages. While US trade with China fell sharply last year, imports from Vietnam, Taiwan and Mexico swelled.

For many companies, making their supply chains more resilient has meant spreading out production around the world, not concentrating it in the United States, said Chris Rogers, a global trade and logistics analyst at Panjiva. "If you want to hedge your risks, you need to stay global," he said.

Michael Upchurch, chief financial officer of Kansas City Southern, which runs railroads through Mexico and the US, said in an earnings call this year that more companies were eyeing Mexico for new facilities because of the tariffs on China and Mexico's relatively low wages and proximity to American customers. Building new factories would take time, he said, "but over the next few years, we would certainly expect to see benefit."