First Read is a morning briefing from Meet the Press and the NBC Political Unit on the day's most important political stories and why they matter.

The most important number in the new NBC/WSJ poll

There are plenty of storylines and new numbers from our latest national NBC/WSJ poll, but here’s maybe the most important number of all: 51% -- as in President Obama’s approval rating, which is his highest mark in the poll since his second inauguration. Why is it important? Because it means that Obama will be an asset to Hillary Clinton on the campaign trail unlike he was in the 2014 midterms, when his approval rating was in the low 40s. And consider his approval rating among these key parts of the Democratic base and swing groups:

Of course, an incumbent president with a 50%-plus job-approval rating isn’t a guarantee for a party keeping the White House -- see 2000. But it’s certainly better than what Republicans experienced in 2008, when George W. Bush’s rating was 27% in our April 2008 NBC/WSJ poll. Our current poll found only 39% saying they would consider voting for Obama if he could run for a third term, but it’s higher than the 34% who said this about Bill Clinton in Sept. 2000. And 78% of African Americans, 72% of Democrats, 62% of Latinos, and 50% of those ages 18-34 said they would consider voting for Obama again if they could.

Donald Trump, conspiracy-theorist-in-chief?

Last night, the Washington Post wrote how Donald Trump described the 1993 suicide of White House aide Vince Foster as “very fishy.” From the Post: “When asked in an interview last week about the Foster case, Trump dealt with it as he has with many edgy topics — raising doubts about the official version of events even as he says he does not plan to talk about it on the campaign trail. He called theories of possible foul play ‘very serious’ and the circumstances of Foster’s death ‘very fishy.’” This isn’t the first time that Trump has dabbled in conspiracy theories. There’s the 2011 “birther” crusade against President Obama; there’s the allegation that Ted Cruz’s father was with Lee Harvey Oswald; and there’s Trump flirting with the idea that the late Supreme Court Justice Antonin Scalia might have been murdered. As MSNBC's Benjy Sarlin wrote earlier this month, “[Trump], whether by choice or by nature, appears fundamentally unable to distinguish between credible sources and chain e-mails. Equally significant, though, is that he uses these falsehoods to elevate fringe conspiracy theories and anecdotes that politicians are normally careful to keep far away from mainstream politics. He’s spread discredited claims linking vaccines to autism, for example — a debunked theory that medical officials say has harmed efforts to wipe out preventable diseases.”

Clinton camp highlights Trump’s past comment rooting for housing market to collapse

The Clinton campaign is out with a new media blitz, including a web video, to criticize Trump’s comment in 2006 that seemed to be rooting for the housing market to collapse so he could make money. “I sort of hope that happens, because then people like me would go in and buy. If there is a bubble burst, as they call it, you know you could make a lot of money.” The Washington Post: “About a dozen surrogates and local elected officials in Ohio, Virginia, Pennsylvania, Florida, New Hampshire, Iowa, Colorado, Nevada and elsewhere will host calls, events and release statements focused on Trump’s response to the housing crisis that precipitated the economic recession. Sen. Tim Kaine (D-Va.) and Rep. Tim Ryan (D-Ohio), will be engaged in the efforts and Ryan will host a conference call with reporters at noon Tuesday to hammer home the message. ‘You don't make America great by rooting for its economy to fail,’ Ryan said in a statement.”

Trump vs. Clinton on the issues

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Why is the Clinton camp focused on that 2006 comment? One reason is that -- at least right now -- Trump has the advantage on the economy and Wall Street, according to our latest NBC/WSJ poll.

61% have reservations or are uncomfortable with Trump being first American president without previous experience in government or the military

Here are a final set of numbers from our NBC/WSJ poll: Six-in-10 American voters say they’re unsure about Trump’s lack of government or military experience, including 42% who say they are VERY uncomfortable with it. “To put that number in context: A lower total percentage of voters - 51 percent - expressed concern about Bernie Sanders potentially becoming the first self-described Democratic socialist to lead the country. Those who expressed concern about Trump's lack of military or government experience included 68 percent of women, 60 percent of independents, 78 percent of undecided voters and about a third of Republican primary voters,” one of us writes.

Sanders: Of course the Democratic convention will be “messy”

In an interview with NBC's Kristen Welker, Bernie Sanders attempted to clarify what he meant by saying that the Democratic convention in Philadelphia would be "messy." Sanders told Welker, “Well, of course, it will be. That’s what democracy is about. But if you use the word ‘messy,’ it means that people will be engaged in vigorous debate. We don’t have that often in the U.S. But I think that’s what a convention is about. I happen to believe that we should have a national health-care system offering health care to all people. Secretary Clinton disagrees. I hope there will be a vigorous debate.”

Our question: Hasn’t there already been a debate over Sanders’ and Clinton’s policies, and isn’t Clinton ahead in the vote totals? Here’s the current delegate math in the Democratic race:

In pledged delegates, Clinton currently holds a lead of 274 delegates

Clinton 1,771 (54%)

Sanders 1,497 (46%)

Clinton must win 32% of remaining pledged delegates to get a majority in pledged delegates

Sanders must win 68% of remaining pledged delegates to get a majority in pledged delegates

In overall delegates (pledged + super), Clinton holds an overall lead of 762 delegates

Clinton must win 9% of remaining delegates to reach 2,383 magic number

Sanders must win 91% of remaining delegates to reach 2,383 magic number

Terry McAuliffe under investigation

Finally, NBC’s Pete Williams reports: “Federal officials say the FBI has been looking at whether Terry McAuliffe's 2013 campaign for governor of Virginia accepted political contributions that were forbidden by federal law. McAuliffe is a close friend of the Clintons and a former chairman of the Democratic Party and co-chairman of Hillary Clinton's 2008 campaign. But officials say that's not a focus of the investigation. McAuliffe is a one-time board member of the charitable foundation set up by former president Bill Clinton, and records show 120 donors contributed to both the foundation and McAuliffe's campaign. Federal officials say investigators are looking at those overlaps -- and are especially interested in contributions from Wang Wenliang, a Chinese politician. Contributions by foreign nationals are barred, but a spokesperson for Wang says he has permanent US resident status and that his contributions were legal. An expert on campaign law says the FBI may be looking at whether the money Wang gave came from a Chinese-based company he runs, which would be illegal.”

On the trail

Hillary Clinton campaigns throughout California… So does Bernie Sanders… Donald Trump holds a rally in Albuquerque, NM at 9:00 pm ET… And Bill Clinton also is in New Mexico. Don’t forget to check out the political unit’s rolling minute-to-minute coverage of all the latest 2016 developments at the On the Trail liveblog at NBCNews.com.