With the U.S. presidential primaries underway, everyone is wondering whether President Donald Trump will be re-elected in November. Opinion polls show that the ability to beat Trump ranks high among Democratic primary voters' top priorities. Following Trump's acquittal in the Senate on impeachment charges and a State of the Union address in which he could tout America's strengths — first and foremost, the economy — the president's approval rating, at 49 percent, is the highest since he took office.

But Trump has reason for concern. The acquittal may offer merely a transitory bump and his approval rating should be much higher than it is, given the state of the economy.

Consider the precedent of President George H.W. Bush, whose approval rating rose to 91 percent following the Persian Gulf War, which had received congressional approval, succeeded in expelling Iraqi President Saddam Hussein's forces from Kuwait, and was partly paid for by America's allies (including Saudi Arabia, the United Arab Emirates, Germany and Japan).