The Globe and Mail reports in its Friday edition that U.S. President Donald Trump's promise to secure the Strait of Hormuz appears increasingly unrealistic as Iran tightens its grip on the vital waterway. The Globe's Rita Trichur writes that recent drone and missile attacks on oil and gas tankers have led to heightened shipping insurance costs and cancellations. The strait has effectively been closed since Saturday. Ongoing attacks on vessels only add to the skepticism surrounding Mr. Trump's vow to ensure its security. Mr. Trump is underestimating the determination of Iran's Islamic Revolutionary Guard Corps to control the strategic waterway for 20 per cent of global oil and gas shipments. Concerns are growing that the U.S. is depleting its weapon stockpile in this conflict. The IRGC has been doubling down on defiance since Mr. Trump unveiled his ill-defined security plan for the strait in a social-media post. Mr. Trump's security promise for the Strait of Hormuz lacks credibility because of his own record of reneged commitments. There is a risk that Mr. Trump is spreading the U.S. military too thin by waging a separate war against Iran. Thus, his security guarantees for the Strait of Hormuz are utterly implausible.