WASHINGTON—After moving to the precipice of military action against Iran, President Trump finds himself caught between negotiations that show few signs of yielding a nuclear deal and a war he is reluctant to join.

Negotiating with Tehran is time-consuming and difficult under the best of circumstances. And it remains unclear whether President Trump’s 14-day clock is more than a way to buy time for military preparations.

Trump said he was waiting to see “whether or not people come to their senses.”