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.

Obama: “What I think is scary is a president who doesn’t know their stuff”

PHILADELPHIA -- Four years ago, Bill Clinton served as the explainer-in-chief testifying for President Obama’s re-election bid. Tonight when he addresses the Democratic convention here, expect Obama to return the favor for Hillary Clinton, serving as a character witness for her. But also expect Obama’s speech to be a political indictment of Donald Trump. “What I think is scary is a president who doesn't know their stuff and doesn't seem to have an interest in learning what they don't know,” Obama told NBC’s Savannah Guthrie in an exclusive interview on “Today this morning. “If you listen to any press conference [Trump’s] given or listen to any of those debates, basic knowledge about the world or what a nuclear triad is or where various countries are … those are things that he doesn't know and hasn't seemed to spend a lot of time trying to find out about.” When Guthrie asked Obama what he hopes the headline of his speech tonight will be, he answered, “I hope my headline is that the president of the United States is profoundly optimistic about America's future -- and is 100% convinced that Hillary Clinton can be a great president.” It will be interesting to see how if/how Trump responds to Obama’s speech, especially given how he’s gotten under Trump’s skin the past (see the 2011 White House Correspondents Dinner).

It was exactly 12 years ago today when Obama addressed the 2004 Dem convention

For more on Obama, don’t miss this earlier piece on why he might be the most important player in this entire election, as well as this article by NBC’s Perry Bacon about how Obama has reshaped the Democratic Party. And as NBC’s Bradd Jaffy reminds us, today is the 12th anniversary of Obama’s 2004 keynote address at the Democratic convention, where he stated, “I say to them tonight, there’s not a liberal America and a conservative America — there’s the United States of America.”

Day Three’s lineup

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In addition to Obama, tonight’s other featured speakers include Vice President Biden, VP pick Tim Kaine, former Defense Secretary Leon Panetta, former NYC Mayor Michael Bloomberg, former Rep. Gabby Giffords and her husband Mark Kelly, and families of the victims of the Newtown and Orlando shootings.

Humanizer-in-Chief: Bill Clinton talks about his love story with Hillary

As for Bill Clinton’s speech last night, here’s the take from NBC’s Leigh Ann Caldwell: “In his turn on the Democratic National Convention stage Tuesday night, former president Bill Clinton gave a deeply personal account of his wife, newly-minted Democratic nominee Hillary Clinton. It was an attempt to both introduce and remind voters of her decades-long resume of service as a practicing lawyer, first lady, senator and secretary of state. It was a historic day, but the former president stayed away from highlighting the monumental achievement of his wife becoming the first woman to win a major-party nomination. Instead, he spoke of the early days of their relationship and chronicled a litany of achievements in Hillary Clinton's 40-year career.”

On Tim Kaine’s big speech

It speaks to the star attractions in Philly -- Obama and Biden tonight, Bill Clinton last night -- that we’re now just getting to VP pick Tim Kaine, who addresses the Democratic convention this evening. Kaine’s rollout on Saturday in Miami was a success for the Clinton campaign, but that even quickly got overshadowed by the Debbie Wasserman Schultz/DNC/WikiLeaks story. And Kaine’s speech tonight will be the biggest of his life. Many Americans still don’t know who he is.

A Tale of Two Different Conventions

Two days in, and it’s easy to conclude just how thematically different the Democrats’ convention has been from last week’s GOP convention in Philadelphia. The Democrats’ Night One was about Bernie Sanders (in trying to unifying the party) and First Lady Michelle Obama (who reminded the audience that the country is already great). Night Two, after a well-choreographed roll-call vote, was all about humanizing Hillary Clinton, and was capped off by a testimonial from her husband Bill. Tonight’s Night Three -- headlined by President Obama, Vice President Biden, and VP pick Tim Kaine -- is set to emphasize the importance of being commander-in-chief, according to a Clinton campaign official. And tomorrow’s Night Four features Hillary Clinton formally accepting the Democratic presidential nomination. By contrast, here were the themes of Donald Trump’s GOP convention last week:

GOP’s Night One: national security, Benghazi, victims of violence committed by immigrants, Rudy Giuliani and Melania Trump.

GOP’s Night Two: GOP politicians who made the case against Clinton, and Trump’s families and friends who made the case for him.

GOP’s Night Three: Ted Cruz (who didn’t endorse Trump), Newt Gingrich, and VP nominee Mike Pence.

GOP’s Night Four: Ivanka Trump and Donald Trump.

Terry McAuliffe’s “Kinsley” gaffe

Politico: “Virginia Gov. Terry McAuliffe, longtime best friend to the Clintons, said Tuesday that he believes Hillary Clinton will support the TPP trade deal if elected president, with some tweaks. ‘I worry that if we don’t do TPP, at some point China’s going to break the rules -- but Hillary understands this,’ he said in an interview after his speech on the main stage at the Democratic National Convention. ‘Once the election’s over, and we sit down on trade, people understand a couple things we want to fix on it but going forward we got to build a global economy.’” A McAuliffe spokesman later walked back the comment, and the Clinton camp’s John Podesta tweeted, “Love Gov. McAuliffe, but he got this one flat wrong. Hillary opposes TPP BEFORE and AFTER the election. Period. Full stop.” But the damage was already done, and it could be a problem over the next two days. (Did McAuliffe not see all of the anti-TPP signs in the arena?) This was a clear “Kinsley” gaffe -- saying something that’s actually true. And that’s why it could leave a mark. And don’t be surprised if Trump tries to seize on it more today. This just in: NBC’s Andrea Mitchell spoke with McAuliffe, who said he was simply saying that President Obama and the governors want TPP, and that Hillary Clinton would work to make the changes necessary to make it a better deal.

On the trail

Donald Trump and Mike Pence campaign together in Scranton, PA at 3:00 pm ET… Trump later holds a rally in Toledo, OH at 8:00 pm ET, while Pence has an event in Wisconsin at 8:00 pm ET.