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

It’s 48 -- the percentage of Americans approving of President Obama’s job. Why is that number important? Because the poll shows -- once again -- how Hillary Clinton and Obama are inextricably tied together. And so an Obama approval in the high 40s is good news for Hillary’s general-election prospects (see her current leads in the poll against Jeb Bush, Marco Rubio, and Scott Walker), and an Obama approval in the low 40s is bad news (like we saw in 2014). To see how Obama and Hillary are tied to each other, just consider the favorable/unfavorable ratings for each.

Overall: Obama 45%-41%, Clinton 44%-40%

Men: Obama 42%-44%, Clinton 35%-48%

Women: Obama 47%-39%, Clinton 52%-34%

African Americans: Obama 86%-2%, Clinton 81%-3%

Latinos: Obama 53%-28%, Clinton 51%-22%

18-34: Obama 53%-26%, Clinton 46%-27%

Whites: Obama 37%-50%, Clinton 37%-48%

Democrats: Obama 81%-11%, Clinton 75%-10%

Independents: Obama 36%-40%, Clinton 34%-40%.

Obama performs slightly better among men; Hillary performs better with women. Obama does slightly better with those ages 18-34; Clinton performs slightly better with whites. But outside those MINOR differences, their numbers are essentially the same. And that dynamic is so important to understand when it comes to a general election a year and a half from now. Oh, and don’t forget this: George W. Bush’s approval rating at this same point in time heading into the 2008 contest was 29%.

How Hillary outperforms a generic Democratic presidential candidate

Here’s another important dynamic to understand: Hillary Clinton outperforms a generic Democratic presidential candidate. While she leads Bush/Rubio/Walker between 8-14 points, a generic Democratic presidential candidate barely beats a GOP generic candidate, 39%-36%. And the difference comes from the key Democratic-leaning demographic groups. A generic Democrat has a 16-point lead among those 18-34 (46%-30%), but Hillary’s average lead over Jeb and Rubio here is 29 points (58%-29%). A generic Democrat has a 62-point lead among African Americans (69%-7%), but Hillary’s lead against Bush/Rubio here is 87 points (91%-4%). And a generic Democratic candidate holds a 9-point lead among Latinos (40%-31%), but Hillary’s average here against Jeb/Rubio is 42 points (65%-23%).

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Bernie’s Bounce

Last week, we were careful to explain that “Bernie-mentum” said more about his standing compared with Martin O’Malley/Jim Webb/Lincoln Chafee than with Hillary Clinton. And here’s the reason why: Hillary holds a whopping 60-point lead (!!!) over Sanders in the NBC/WSJ poll, 75%-15%. Nevertheless, the survey shows that Bernie has had a nice bounce since getting into the Democratic race. Back in March, the poll found 21% of Democratic primary voters saying they could support him, versus an equal 21% who said they couldn’t. Now? It’s 40% support, 32% not support. Maybe more importantly for Sanders (as well as O’Malley/Webb/Chafee), he easily tops the Democratic field when it comes to 2nd choice.

Bounces for Huckabee, Carson, and Fiorina

And it’s just not Bernie Sanders getting a bounce. According to our poll, 65% of Republican primary voters say they could see themselves supporting Mike Huckabee (who announced his campaign on May 5) -- up 13 points since our April NBC/WSJ poll. In addition, 50% of them could support Ben Carson (who announced May 4) -- up 11 points. And 31% could support Carly Fiorina (May 4) -- up 14 points. One of the biggest questions we have is the size of Scott Walker’s bounce when he announces his presidential bid next month.

Republicans are from Mars, Democrats are from Venus

If you want further evidence that today’s two major political parties couldn’t be further apart from each other, just consider these numbers in our NBC/WSJ poll:

54% of Republicans say a decline in moral values is their top/second biggest concern, versus just 16% of Democrats who say this;

38% of Republicans say terrorist attacks is their top/second biggest concern, versus only 17% of Democrats who say this;

39% of Democrats say the wealthy having too much influence is their top/second biggest concern, versus 21% of Republicans who say this;

42% of Democrats say the shrinking middle class is their top/second biggest concern, versus just 5% of Republicans;

35% of Democrats say climate change is their top/second biggest concern, versus just 3% of Republicans who say this.

The Confederate flag -- and the power of change

Yes, we understand that removing the Confederate flag is largely symbolic in the wake of the Charleston church shootings. Still, talk about change happening pretty quickly. In addition for South Carolina Gov. Nikki Haley and Sens. Tim Scott and Lindsey Graham calling for the removal of the flag from the statehouse grounds, Walmart says it’s removing all items that promote the Confederate flag. And last night, Mississippi’s House speaker called to remove the Confederate emblem from its state flag. But keep this in mind: South Carolina’s legislature voting to remove the Confederate flag isn’t a slam dunk. As one plugged-in South Carolina GOP operative emailed us, “If they find some mechanism to take a vote in the next week or two, I think there is a decent shot because no one (or very few people) will want to be on record opposing its removal right now. The more time passes the less chance there is.”

Hillary to make appearance near Ferguson, MO

“Democratic presidential candidate Hillary Clinton will be in St. Louis on Tuesday for a campaign and fundraising swing,” the St. Louis Post-Dispatch writes. “Clinton’s campaign officials said Monday that the former secretary of state and U.S. senator will participate in a Tuesday afternoon ‘community meeting’ at Christ the King United Church of Christ in Florissant. It will be hosted by the Rev. Traci Blackmon. ‘The conversation will address the massacre in Charleston and broader issues around strengthening communities,’ a statement from Clinton’s campaign said. The event will place Clinton within a few miles of last year’s Ferguson unrest, a series of events that spurred a national conversation on race.”

Big trade vote in the Senate

Finally, today is the big (renewed) trade vote in the U.S. Senate. The New York Times: “The Senate on Tuesday is set to vote for the second time on a motion to cut off debate on legislation that would grant President Obama enhanced negotiating powers to complete a major Pacific trade accord, but this time the bill is shorn of a measure to assist workers harmed by such agreements. If supporters can muster the 60 votes they need, final passage on Wednesday of so-called trade promotion authority is all but assured, putting intense pressure on House Democrats.” Momentum appears to be on the pro-trade side. “It’s looking increasingly like those House Dems and liberals — who had previously opposed TAA as a way to kill Fast Track — may have been backed into a corner and may have no choice but to support TAA in the end,” the Washington Post Greg Sargent writes.