The Note: A nation reels as mass shooting strikes Las Vegas

— -- THE TAKE with ABC News' Rick Klein

This weekend would suggest that there is little or nothing exempt from the politics of division, as practiced by President Trump. Now comes a fresh test – the worst mass shooting in U.S. history, not to mention the Trump presidency, at a country-music festival in Las Vegas overnight. The ensuing days will test the president's tone, and – depending on what's learned about the shooter and his motivations – is very likely to involve the president's name in some way. Can he resist the urge to punch – or counter-punch – in a time of national tragedy, compounded by an unfolding crisis in Puerto Rico? These types of stories always wind up being political, whether it's about gun control or the sources of the dark forces in a gunman's life. There's a numbing familiarity to it all. What's new to the equation is Trump, whose instincts have rarely taken him in the direction of unity. The president spent the weekend being defiantly Trump, even down to his golf-course routine. This week will challenge him to recognize what this moment calls for.

WHAT YOU NEED TO KNOW TODAY

QUOTE OF THE DAY

"Tragic & heinous act of violence has shaken the #Nevada family. Our prayers are w/ the victims & all affected by this act of cowardice." --Nevada Gov. Brian Sandoval on Las Vegas mass shooting

‘POWERHOUSE POLITICS' PODCAST

ABC News' Rick Klein and Jonathan Karl hear from two very different perspectives on the Roy Moore win in the Alabama Republican runoff and what's ahead for the GOP in the 2018 midterms. Senate Conservatives Fund President Ken Cuccinelli wants Senate leader Mitch McConnell out now. Former Republican National Committee Spokesman Doug Heye warns of another Christine O'Donnell moment. http://apple.co/21V9721

NEED TO READ

Trump slams Puerto Rico mayor, says "they" want everything "done for them." President Donald Trump slammed the mayor of Puerto Rico's capital city for "poor leadership" a day after the mayor criticized a Trump administration official's positive assessment of the situation in the hurricane-ravaged U.S. territory. Trump also suggested politics lay at the heart of the critical comments by San Juan Mayor Carmen Yulín Cruz, claiming that she has "been told by the Democrats that you must be nasty to Trump." http://abcn.ws/2kbdHj7

San Juan mayor says focus needs to be on ‘saving lives,' not Puerto Rico's debt. The mayor of San Juan, Puerto Rico, whom President Donald Trump slammed on Twitter for "poor leadership," said she would meet with the president when he visits the island Tuesday if she is invited to do so. Mayor Carmen Yulín Cruz also told ABC News Chief Anchor George Stephanopoulos on "This Week" that with the devastation wrought by Hurricane Maria, the focus should be on "saving lives" and not the U.S. territory's high rate of debt or what it may cost to rebuild. http://abcn.ws/2hEyWc7

Trump dedicates golf trophy to hurricane victims amid controversy over response. President Trump dedicated the trophy of the Presidents Cup golf tournament to hurricane victims in Texas, Florida and Puerto Rico, telling the crowd he wanted the focus on those who "have really suffered." Trump, the tournament's honorary chairman and the first sitting president to attend the final day's matches, made the remarks as he presented the gold trophy. http://abcn.ws/2yinIBc

Treasury chief dismisses concerns that Trump may personally benefit from tax plan. ABC News Chief Anchor George Stephanopoulos pressed Treasury Secretary Steve Mnuchin in an interview on "This Week" Sunday on how the public will know whether Trump would benefit from the tax proposal if the president won't release his tax returns. Mnuchin responded, "I think the American public will be comfortable with the information they have." "There's going to be full transparency as we go through the legislative process, what those rules are, so that rich people can't take advantage of it," the treasury secretary said. http://abcn.ws/2ygNhCL

In Puerto Rico's remote regions, tears of relief when aid comes. ABC News

VA chief took in Wimbledon, river cruise on European work trip; wife's expenses covered by taxpayers. The Washington Post

Rep. Steve Scalise on surviving: "It's a miracle." CBS News

The Note is a daily ABC News feature that highlights the key political moments of the day ahead. Please check back tomorrow for the latest.