Ten Democratic presidential candidates offered contrasting views on the biggest threats facing the U.S. in their first debate Wednesday.

While multiple Democrats highlighted China and the global threat of nuclear proliferation as major challenges, no two candidates gave the same answer when asked to identify the greatest geopolitical threat America currently faces.

Four candidates — former Maryland Rep. John Delaney, Minnesota Sen. Amy Klobuchar, former Housing and Urban Development Secretary Julian Castro and Ohio Rep. Tim Ryan — mentioned China in their answers.

Though they were denied time to explain their answers, the focus on China signals broad bipartisan concern about the Asian nation's rapid rise into a global superpower.

Yet even as President Donald Trump traveled to the G-20 summit in Osaka, Japan, to meet with Chinese President Xi Jinping in hopes of salvaging a trade deal on the rocks, none of the Democratic contenders brought up trade in the debate.

Negotiations between Beijing and the U.S. broke down in May, as the two countries imposed new tariffs on billions of dollars' worth of each other's goods. Current and former Trump administration officials say the meeting between Trump and Xi could revive the stalled trade talks.