American voters are set to cast their ballots on Tuesday after a tumultuous election cycle that could make Kamala Harris the first female president in U.S. history or grant Donald Trump a stunning comeback that could reverberate globally.

As polling stations across the nation open on Election Day, the race between Democratic Vice President Harris, 60, and Republican former President Trump, 78, is too close to call, reflecting the most contentious and unpredictable presidential race in recent history.

In the final hours of their campaigns, the fierce adversaries are focused on mobilizing their supporters and appealing to undecided voters in key swing states that will likely determine the election’s outcome.

This campaign has been marked by a series of shocking developments, including Harris’s sudden entry into the race following President Joe Biden’s withdrawal in July and Trump enduring two assassination attempts alongside a criminal conviction. Yet, none of these events have shifted the tight race reflected in opinion polls.

Polling stations open at 6:00 a.m. EST (1100 GMT), with tens of millions expected to vote in person, adding to the over 82 million who have already participated in early voting over the past weeks. Given the close nature of the contest, official results may take several days to finalize, intensifying the anxiety in an already polarized nation.

Concerns are growing about potential unrest and violence if Trump loses and subsequently disputes the results, as he did in 2020. Security measures, including barriers around the White House and boarded-up businesses in Washington, D.C., are being implemented in anticipation of possible turmoil.

Globally, observers are closely watching the election, as its outcome could significantly impact issues such as conflicts in the Middle East, Russia’s ongoing war in Ukraine, and global efforts to address climate change, which Trump has previously dismissed as a hoax.