As Donald Trump marches towards the Republican nomination for President, it’s worth taking a moment to think about which companies would be most affected by four, or even eight, years of a Trump presidency.

One of the most obvious companies to benefit would be oil supermajor BP (LSE: BP). In 2015 BP brought in $74bn of its $222bn in revenue from the US, refined over 700,000 barrels of oil a day at its three refineries and operated 7,000 retail outlets in the country. Trump’s proposal to cut the headline corporate tax rate from 39% to 15% would be a huge boon for BP. Likewise, any increased tensions in the Middle East resulting from Trump’s often bellicose foreign policy positions would likely drive up crude prices to BP’s benefit. Even without Trump in the White House, BP is in good shape as downstream assets bring in record profits, operating costs come down and expenses related to the Gulf of Mexico spill slowly tail off.

Security drive

One of the most notorious of Trump’s mooted policies, the deportation of many of the 11m undocumented workers in the US could end up benefitting private security companies such as G4S (LSE: GFS). G4S brought in 24% of 2015 revenue from North America and already has contracts in America for border protection, running prisons and repatriating deportees, all of which would see spending increases in a Trump presidency. However, with £1.7bn in net debt at year-end, a series of controversies following the company in several jurisdictions and continuing restructuring charges, I would look elsewhere to profit from Trump’s proposals.

Building bridges

Trump’s plan for a $1trn infrastructure investment would certainly benefit CRH (LSE: CRH), the largest building materials provider in the US. CRH produces and sells concrete, asphalt and other materials that would be put to use in the roads, bridges and airports Trump intends to build. CRH already brought in 19% of operating profits from the US last year and will be in good shape no matter who the next president is, as each of the three remaining candidates have pledged major infrastructure projects. Although net debt stood at three times EBITDA at year end, this was due to the wise €6.5bn purchase of assets being divested by Lafarge and Holcim in order to meet regulatory approval for their merger.

A risk too far?

Defence spending is supposedly set to decrease under Trump as he talks of weeding out bloated contracts, which would hurt the major contractors that provide large, multi-year projects. But one company that could benefit is Chemring (LSE: CHG), a maker of countermeasures and other defence products that are mainly used in combat situations. The end of the Iraq and Afghanistan wars has hit Chemring hard, but if Trump’s aggressive policy statements come to fruition and a slimmed-down US military sees more combat, Chemring would undoubtedly sell more missile defence flares and IED detectors. However, even a Trump presidency sending more contracts to Chemring wouldn’t be enough for me to buy shares. The main culprit is £154m in net debt that the company raised £80.8m in a rights issue to help pay down. Even with net debt down to a manageable 1.5 times EBITDA after this share dilution, the company is facing slow growth for the foreseeable future that will constrain shareholder returns.

Of course, history has shown that changing presidents has little effect on stock market returns in the US, much less here in the UK. Investors are much better off looking for high quality companies that perform year in and year out, such as those detailed in the Motley Fool's latest free report, Five Shares To Retire On.

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Ian Pierce has no position in any shares mentioned. The Motley Fool UK has recommended BP. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.