President-elect Donald Trump exploded a half-century of U.S. nuclear-arms policy in a single tweet last week: “The United States must greatly strengthen and expand its nuclear capability until such time as the world comes to its senses regarding nukes.” With that one vague message, Donald Trump, who hasn’t even taken office yet, may have started a new arms race.

Trump’s statement set off alarms around the world, necessitating a cadre of his inner circle to flood the airwaves with now-routine attempts to explain what their boss “really meant.” On MSNBC, Rachel Maddow confronted former Trump campaign manager and newly appointed Trump counselor Kellyanne Conway about the shocking tweet:

Maddow: “He’s saying we’re going to expand our nuclear capability.”

Conway: “He’s not necessarily saying that -”

Maddow: “... He did literally say we need to expand our nuclear capability -”

Conway: “...What he’s saying is...we need to expand our nuclear capability, really our nuclear readiness, our capability to be ready for those who also have nuclear weapons.”

The next morning, during a commercial break on the MSNBC program “Morning Joe,” Trump spoke by phone with Mika Brzezinski, as she and her co-host Joe Scarborough sat in pajamas on the Christmas-themed TV set. The call was not broadcast, but when the show came back from the break, Brzezinski quoted Trump as saying, “Let it be an arms race ... we will outmatch them at every pass and outlast them all.”

Minutes after that aired, Annie Leonard, executive director of Greenpeace USA, told us on the “Democracy Now!” news hour: “Every day, Trump says something that makes us worried, but this may be the most terrifying yet. A nuclear-arms race is the last thing that the world needs. I think about climate change. I think about economic inequality. I think about all of these major threats that we’re facing as a country and as a world. Why would we add on top of that a totally manufactured, unnecessary threat?”

President Barack Obama delivered his first address on the U.S. nuclear arsenal on April 5, 2009, in Prague: “Today, the Cold War has disappeared, but thousands of those weapons have not. In a strange turn of history, the threat of global nuclear war has gone down, but the risk of a nuclear attack has gone up. More nations have acquired these weapons.” Then, in 2016, he proposed a 30-year, $1 trillion dollar nuclear arsenal modernization program. When asked about Obama’s record, Annie Leonard told us, “Greenpeace and many of our allies fought against President Obama’s military spending, and we will fight against President Trump’s military spending.”

While Obama’s nuclear spending continues what Albert Einstein called, in 1946, the “drift toward unparalleled catastrophe,” it still adheres to the current in-force nuclear-reduction treaty between the U.S. and Russia, called New START. This calls for the reduction in the number of warheads in both nations’ stockpiles from the current amount of roughly 7,000 warheads each, to 1,550 warheads each by February 2018. Trump’s declarations suggest he would scrap New START and relaunch a new nuclear-arms race between the U.S. and Russia. This, in turn, could easily trigger the desire among other existing nuclear states, like India, Pakistan and Israel, to increase their stockpiles. Trump also repeatedly stated throughout the presidential campaign that he supports the acquisition of nuclear weapons by other nations, including Japan, South Korea and Saudi Arabia. And he has said the opposite on other occasions, which only highlights the volatility and unpredictability of this incoming commander in chief. In such an unstable world, with an increasing number of nuclear weapons, the likelihood only increases that someone, somewhere will hit the button.

Alarmed at the recent developments, one group has launched a petition urging the current president to take action. “With the stroke of a pen, President Barack Obama could take our nuclear missiles off high alert, making sure that President Trump could not launch them rashly,” writes Joe Cirincione, president of the Ploughshares Fund, a global security foundation. “Trump will have the unfettered ability to launch one or one thousand nuclear warheads whenever he pleases. Four minutes after he gives the order, the missiles will fly. No one can stop him, short of a full-scale mutiny. Once launched, the missiles cannot be recalled.”

Yes, Obama should take the weapons off high alert, but that’s not enough. Donald Trump’s finger on the nuclear trigger is a terrifying prospect. It’s the anti-nuclear movement that needs to go on high alert to make sure that trigger never gets pulled.