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The appalling ambush of Dallas police officers Thursday night delivered another breathtaking body blow to a nation reeling from a summer marked by terrorism, violence and the unsettling sense that events are hurtling out of control.

The attack that left five officers dead and seven wounded happened as protesters gathered peacefully in downtown Dallas to lament the shooting deaths of two young black men by police this week — Philando Castile in Minnesota and Alton Sterling in Louisiana. President Obama's stern reminder that "blue lives" matter, too, as he grieved the two men Thursday turned tragically prescient as videos of the Texas attack surfaced a few hours later.

Protesters who came to demand police accountability instead found their lives suddenly dependent on the courage of those in the "thin blue line." In the footage, officers heroically rushed into the chaos and the fusillade of shockingly well-aimed bullets near the city's well-known Dealey Plaza. The blood shed by these officers, including one from the city's transit patrol, should be a reminder that the push for police accountability must not be divorced from deep respect for those who serve.

This is a dangerous job every hour of every shift, a reality underscored by the FBI's annual compilation of law enforcement deaths. Fifty-one officers "were feloniously killed" in the line of duty in 2014. In 46 of those deaths, offenders wielded firearms. Thirty-five of the officers were wearing body armor when they died.

It's difficult to recall a time when the onslaught of tragic news has been so relentless. Many people understandably feel overwhelmed. Unceasing terrorist attacks at home and abroad have made ordinary places seem vulnerable. The steady drumbeat of young black men's deaths at the hands of law enforcement has broadened a bitter racial divide. Regrettably, this divide will only deepen as details emerge about the Dallas shooter, who said during a fatal standoff with police that he "wanted to kill white people, especially white officers." Police have arrested three others.

Americans' lack of confidence in the leading Republican and Democratic presidential candidates also underscores the unease that many share about the nation's future. It is tempting to go numb or even fall into despair.

Those are exactly the wrong responses, for it is these emotions that cause good people to stand silent when leadership and reforms are sorely needed. Others who are weak-minded may come to more dangerous conclusions — that civil rights must be jettisoned to restore order, for example. Or even that justice is found at the end of a sniper's rifle.

It's important to remember the nation's founders labored to build a system of governance sturdy enough to survive the stress tests the future would surely throw at it. That America just celebrated its 240th birthday — which required it to endure a civil war, two world wars, a great depression and the tumultuous 1960s — is a testament to their vision.

What's needed now are leaders who inspire Americans to remember that its strength is found in remarkable unity — an elusive quality that the European Union has struggled for decades to replicate. Officials in Texas admirably rose to the occasion this week, with the city's police chief, mayor and Republican governor calling for healing. "In times like these, we must remember — and emphasize — the importance of uniting as Americans," Gov. Greg Abbott said.

Those running for the nation's top office shouldn't just lament the latest loss of life. They should echo Abbott's call for unity and then lay out a plan to rebuild it.