The Mexican peso is rallying after a tumultuous weekend for Donald Trump

The Mexican peso is rallying on Sunday at the end of a tough weekend for Donald Trump's campaign.

During this election season, the currency has slumped when he was gaining ground in the polls against Democratic rival Hillary Clinton. Trump's tough talk on trade and immigration with America's southern neighbor reduced demand for the peso.

At 7:46 p.m. ET, the peso was up by 1.65% to 18.9853 per dollar, its strongest level in nearly a month. It weakened to a record low in the last week of September.

The second presidential debate is set to begin at 9 p.m. ET in St. Louis.

On Friday, hot-mic footage taped in 2005 showed the Republican presidential nominee boasting about being able to "grab" women "by the p---y" because "when you're a star they let you do it."

And throughout the weekend, several major Republicans - including 2008 nominee Sen. John McCain of Arizona - withdrew their support for Trump. US President Barack Obama said Trump's remarks showed he was "insecure," "not a character trait that I would advise for somebody in the Oval Office."

In a tweetstorm on Sunday morning, Trump blasted "so many self-righteous hypocrites" ahead of Sunday night's presidential debate.