A Donald Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE presidency that successfully enacts many of the Republican nominee’s key policy proposals would cost the U.S. economy $1 trillion, a new analysis showed on Tuesday.

Oxford Economics, an independent global advisory firm, said that a combination of protectionist trade and immigration policies that include deporting many illegal immigrants and building a border wall would severely damage the economy over the next five years.

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“Should Mr. Trump prove more successful in achieving adoption of his policies, the consequences could be far-reaching — knocking 5 percent off the level of U.S. GDP relative to the baseline and undermining the anticipated recovery in global growth,” the report said.

Under its baseline scenario, Oxford Economics expects economic growth to maintain a rate of about 2 percent reaching $18.5 trillion in 2021.

But a string of Trump policy victories would slow growth to near zero in 2019, knocking that figure down to $17.5 trillion.

On the other hand, if Trump's plans are significantly diluted, as would be expected, because he is forced to negotiate with Congress then his presidency would likely have more muted effects on overall U.S. growth.

"The U.S. economy would slow in the near-term amid increased uncertainty, with growth easing to a level around half a percent below baseline during 2017," the report said.

Globally, the effects also diverge across the two scenarios.

If Congress stymies Trump, world growth edges down modestly relative to the baseline by up to a quarter percentage point during 2017.

"Under the adverse scenario, however, the global economy is more badly shaken and growth remains subdued throughout much of the five-year forecast," the report said.