The tragic slaughter of at least 50 innocent Americans will likely reshape the US presidential election by elevating national security and terrorism as major ideological battlegrounds.
Sharp divisions are already emerging in the aftermath between hardline Republican Donald Trump, and more measured Democrats Hillary Clinton and President Barack Obama, over Islamic State-inspired terrorism, Muslims and gun laws.
Without intending to sound callous so soon after such heartbreak, political analysts have warned for months that a big negative event, such as a major domestic terrorist attack or US recession, could shake up the election and debunk the conventional wisdom that Clinton is assured of beating Trump.
In crude political terms, Trump appears poised to use the most deadly shooting in US history as ammunition to ramp up his nationalist agenda against what he terms "radical Islamic terrorism".
The presumptive Republican nominee immediately doubled down on his controversial call for Muslims to be temporarily banned from entering the US.
The 29-year old Muslim suspect, Omar Mateen, was born in New York to Afghani immigrants and pledged allegiance to the Islamic State terrorist group.
"What has happened in Orlando is just the beginning. Our leadership is weak and ineffective. I called it and asked for the ban. Must be tough," Trump tweeted hours after the shooting.
"Is President Obama going to finally mention the words radical Islamic terrorism? If he doesn't he should immediately resign in disgrace!" Trump wrote earlier on Sunday in the US.
Clinton and Obama condemned the assault in Florida as "terror", while also emphasising the "hate" against gays and lesbians at the nightclub.
Likely sensing Trump's divisive anti-Muslim rhetoric heating up, Clinton said Americans must "stand together" and stay "true to our values" in a statement.
Obama urged Americans to "not give in to fear or turn against each other."
The President and his former secretary of state also argued that loose gun laws needed to be tightened to keep violent weapons out of the hands of dangerous people.
Mass shooter Mateen worked in security and owned guns, even though he was previously twice investigated by the Federal Bureau of Investigation for terrorism links.
In contrast to Democrats who want to clamp down on assault weapons, Trump has been endorsed by the powerful National Rifle Association and in the recent past repeatedly falsely warned gun-loving Americans that Clinton wants to abolish the second amendment and "take your guns away".
The Orlando bloodbath comes in wake of the San Bernardino attacks in California last December, when Muslim extremists Syed Rizwan Farook and Tashfeen Malik, both of Pakistani background, massacred 14 people and injured 22 others.
Fear of terrorism has shot to a top concern of American voters. The worry is palpable.
What has happened in Orlando is just the beginning. Our leadership is weak and ineffective. I called it and asked for the ban. Must be tough
— Donald J. Trump (@realDonaldTrump) June 12, 2016
It undeniably shifts the presidential race to a contest on national security between strongman Trump and a more broad-minded Clinton.
On paper, Clinton's experience fighting international terrorism as secretary of state makes her well qualified to deal with the threat.
Yet Trump's muscular and xenophobic posturing may resonate with a large number of anxious Americans, especially in the grieving swing state of Florida.
"We need to keep guns like the ones used last night out of the hands of terrorists or other violent criminals." —Hillary on the FL attack
— Hillary Clinton (@HillaryClinton) June 12, 2016
