After the slaughter at Sandy Hook, a moment that could define Obama's presidency

Barack Obama must channel his visible anguish to tighten America's gun laws

Shaken: President Obama wipes a tear as he speaks about the shootings in Newtown, Connecticut (Reuters)

When Barack Obama confirmed to a shocked nation that most of the victims of the Sandy Hook shootings were "beautiful little kids" as young as six years old, the President paused to regain his composure. The pause, punctuated by an audible drawing of breath and a dabbing away of tears under his left eye, lasted 11 seconds.

President Obama is often criticised for being analytical and aloof – his first term was not fired by the passion that drove his 2008 White House campaign. Yet in the James S Brady Press Briefing Room at just after 3.15pm local time on Friday, there stood a father of two barely able to contain his grief – and anger – at the apparently senseless killing of children still young enough to believe in Father Christmas.

The White House press corps watched in silence as the seconds ticked by before the President gathered himself and returned to his speech. When he did, Mr Obama dabbed away a tear five more times. He spoke of a nation broken-hearted, but his overwhelming emotion seemed to be anger, restrained as he held on to the lectern, his jaw jutting as he promised "meaningful action to prevent more tragedies like this, regardless of the politics".

There are moments in a president's or prime minister's time in office that define their entire career. Some are policy decisions that dominate – such as Tony Blair and Iraq. Others are reactions to events that either capture, or miss, the public mood. George W Bush's hyperbolic cowboy talk was woven throughout most of his first term, after 9/11, but the most memorable, and one that rang so hollow, even then, was his "mission accomplished" speech on board the USS Abraham Lincoln declaring the Iraq war "over" in May 2003.

Watch a recording of Mr Blair's "People's Princess" tribute after the death of Diana today and it seems like laughably over-the-top ham acting. Yet on that morning, hours after she had died, Mr Blair did capture a mood of outward grief that echoed what many in the country were experiencing, in contrast with the cold response of the Royal Family. His premiership, four months old, pivoted on that moment until it turned again after the Iraq invasion.

In the pictures of the President and his inner circle watching the cornering and killing of Osama bin Laden, Mr Obama's face was emotion-free (while Hillary Clinton covered her mouth in shock).

On Friday, the President's tears were believable: the words may have been scripted, but his human response was not rehearsed. The microphone picked up a stifled gulp when he quoted from the Bible, Psalm 147 verse 3, as he pledged to "heal the broken hearted and bind up their wounds".

But everyone knows he needs to do more than that to make his presidency worthwhile. And he must start by bringing in tighter controls on gun use and gun ownership. He has nothing to lose.

If President Obama can overcome opposition and implement tighter gun controls, then those 11 seconds of gathering courage will be a more meaningful legacy than the killing of Bin Laden. They will be the defining moment of his presidency.

slaughter at sandy hook A time for decisive action