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

GOP divisions widen with Trump-vs.-McConnell spat

WASHINGTON — On Monday morning, we wrote how divided Republicans are six and half months into Trump’s presidency, especially after the GOP-led Senate failed in its effort to repeal and replace Obamacare. Well, things have gotten only more divided since then. Consider:

Vulnerable Sen. Dean Heller, R-Nev., now has a GOP primary challenger in Danny Tarkanian;

Politico reports that one of Trump’s top donors, Robert Mercer, is contributing $300,000 to a Super PAC supporting the Republican challenging incumbent Sen. Jeff Flake, R-Ariz;

Sen. Ron Johnson, R-Wis., said in a radio interview that John McCain’s no-vote on health care might have been due to his brain tumor; Johnson has called his remarks “unfortunate” and “clumsy”;

And maybe in the most significant skirmish to date, President Trump is now going after Senate Majority Leader Mitch McConnell. “Can you believe that Mitch McConnell, who has screamed Repeal & Replace for 7 years, couldn't get it done. Must Repeal & Replace ObamaCare!” Trump tweeted this morning.

That Trump tweet — and an earlier one from Wednesday — came after McConnell criticized Trump's "excessive expectations" on health care.

"Our new president, of course, has not been in this line of work before," McConnell said. "I think he had excessive expectations about how quickly things happen in the democratic process."

Politics inevitably produces tension and conflict, even among allies from the same party. Things, after all, weren’t always rosy between Barack Obama’s White House and Harry Reid/Nancy Pelosi. But that Democratic tension never came this early in a presidency — and it certainly never was this public.

Republicans, who control all branches of government, still have plenty on their to-do list — tax reform, passing a budget, funding the government and raising the debt ceiling. But all of those items become much harder to achieve when there’s public conflict between the president and the Senate majority leader.

It’s Democrat vs. Democrat in California

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Yet just to emphasize how Republicans don’t have a monopoly on party divisions, don’t miss this New York Times dispatch on Democrat-vs.-Democrat conflict in California.

“Even at a time of overall success, state Democrats are torn by a bitter fight for the party leadership, revealing the kind of divisions — between insiders and outsiders, liberals and moderates — that unsettled the national party last year and could threaten its success in coming years,” the Times writes.

“The fight pits Eric C. Bauman, a longtime party leader, against Kimberly Ellis, a Bay Area activist. Mr. Bauman won the election by just over 60 votes out of 3,000 cast at the party convention in May, but Ms. Ellis has refused to concede, claiming voting improprieties, like permitting ineligible people to vote for Mr. Bauman.”

More: “The party is expected to issue a final ruling on Ms. Ellis’s allegations by Aug. 20; in an interview, she said she would go to court if the party ruled against her.”

But there’s one difference between Trump vs. McConnell and this Dem-on-Dem fight in California: Republicans were victorious nine months ago, while Democrats are still reeling from their surprise White House defeat. The winning party is always supposed to be more unified than the losing party.

FBI agents searched Paul Manafort’s home

Just to remind you how the Russia story isn’t going away — and only seems to be intensifying — is this news from yesterday: “FBI agents searched one of the residences of former Trump campaign chairman Paul Manafort last month, a dramatic escalation in the special counsel's Russia investigation,” NBC News confirmed.

“The agents ‘executed a search warrant at one of Mr. Manafort's residences,’ Jason Maloni, a spokesman for Manafort, told NBC News. ‘Mr. Manafort has consistently cooperated with law enforcement and other serious inquiries and did so on this occasion as well.’”

Here’s the Washington Post, which broke the story: “The raid, which occurred without warning on July 26, signaled an aggressive new approach by special counsel Robert S. Mueller III and his team in dealing with a key figure in the Russia inquiry. Manafort has been under increasing pressure as the Mueller team looked into his personal finances and his professional career as a highly paid foreign political consultant.”

U.S. has prepared to use B-1 bombers in response to North Korea

As for the rising tensions with North Korea, NBC’s Cynthia McFadden and team report that the Pentagon has prepared the use of B-1 bombers on North Korea’s missile sites. “‘Of all the military options … [President Trump] could consider, this would be one of the two or three that would at least have the possibility of not escalating the situation,’ said retired Adm. James Stavridis, former Supreme Allied Commander Europe and an NBC News analyst.”

“‘There is no good option,’ a senior intelligence official involved in North Korean planning told NBC News, but a unilateral American bomber strike not supported by any assets in the South constitutes ‘the best of a lot of bad options.’”

Strange touts Trump support in new ad, while Brooks hits McConnell

Less than a week to go before the August 15 GOP Senate primary in Alabama, “U.S. Sen. Luther Strange released a new ad on Wednesday touting the endorsement he received less than 24 hours before from President Trump,” AL.com reports.

Meanwhile, Mo Brooks released this statement regarding the Trump-vs.-McConnell spat, per NBC’s Frank Thorp: “The President and I agree on this: McConnell and Luther Strange have failed. It’s time to ditch Mitch and his lackey Luther Strange. Whether you're talking ObamaCare, the Wall, or balancing the budget, the Trump Agenda is dead with McConnell and Strange in the Senate."

Northam leads Gillespie by six points in Virginia, per Quinnipiac poll

A Quinnipiac poll released Wednesday found Democrat Ralph Northam leading Republican Ed Gillespie by six points in Virginia’s gubernatorial contest, 44 percent to 38 percent; Libertarian Cliff Hyra got 4 percent. Trump’s approval rating in the state is at 36 percent, while 51 percent approve of outgoing Democratic Gov. Terry McAuliffe.