The job losses would disproportionately affect lower-income and lower-skilled workers, the report stated.
"Donald Trump advocates policies that could potentially overturn the existing U.S.-led rules-based international trade system," the authors of the 49-page report wrote. "His policies place at risk the livelihoods of millions of Americans, most of whom probably do not think of their jobs as tied to international trade."
The Peterson Institute, a pro-trade think tank based in Washington, called their job-loss estimates conservative and labeled Trump's proposals "irresponsible and reckless."
Trump has upended GOP orthodoxy on free trade by running on a restrictionist platform in an appeal to working-class voters in an election year in which economic anxiety has resonated among both parties. Democratic nominee Hillary Clinton also has moved left on trade, opposing the Trans-Pacific Partnership (TPP), a 12-nation trade pact negotiated by the Obama administration that she had supported while serving as secretary of state.
The Peterson Institute report noted Clinton's opposition to the TPP, which the think tank had previously stated would result in a $77 billion to $123 billion boost to the U.S. economy in its first year if the deal is approved by Congress and implemented.
But Clinton, the authors wrote, has a "nondoctrinaire" record on trade and she "supports strengthened enforcement of existing rules, increased efforts to deal with currency manipulation, and changes in the tax code that eliminate tax loopholes." Clinton has "expressed skepticism about trade but in effect represents stasis."
The opposition to TPP from both major-party candidates has left the world's largest regional trade accord in doubt. Obama pledged last week that he would continue pushing Congress to ratify the deal before he leaves office, and he met with a coalition for trade-friendly business executives and political leaders in the Oval Office.
But Republican leaders in Congress have said a vote on the pact is unlikely this year.