Donald Trump Donald John TrumpObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE is turning his fire to President Obama as he looks ahead to the general election campaign.

Trump’s foreign policy speech in Washington this week speech offered a preview of how he plans to attack Obama and the president’s former secretary of State in the fall, if Trump and Hillary Clinton Hillary Diane Rodham ClintonWhat Senate Republicans have said about election-year Supreme Court vacancies Bipartisan praise pours in after Ginsburg's death Trump carries on with rally, unaware of Ginsburg's death MORE win their respective party nominations.

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Trump forcefully knocked Obama’s strategy in the Middle East and argued the Obama-Clinton foreign policy has been “a complete and total disaster.”

A day later, Trump targeted the Secret Service’s plan to raise the height of the fences bordering the White House to take another shot at Obama.

“President Obama understands that you build strong, tall, beautiful walls to keep people out who don't belong,” he wrote on Facebook.

Going after Obama is nothing new for Trump. He launched his political career by claiming Obama was born in Kenya and therefore ineligible to serve as president, an argument debunked by fact-checkers and the president’s own birth certificate.

Trump has never really stopped attacking Obama on the campaign trail, but the remarks this week still seemed like a shift given the GOP frontrunner’s crushing wins a day earlier in five East Coast primaries.

Those wins led Trump to declare himself the presumptive GOP nominee.

“I think he has pivoted,” Republican strategist Matt Mackowiak said of Trump. “He wants to focus on the general election and, to the extent he’s able to be disciplined, he’s going to focus on Obama and Hillary.

Obama’s approval ratings have risen over the last six months, giving another advantage to likely Democratic nominee Clinton, who most polls suggest is ahead of Trump.

As a result, it’s clear that Trump’s pathway to victory depends in part on knocking Obama back down.

“Our actions in Iraq, Libya and Syria have helped unleash ISIS,” Trump said during this week’s speech at the Mayflower Hotel. “We’re in a war against radical Islam, but President Obama won’t even name the enemy, and unless you name the enemy, you will never ever solve the problem.”

That plan could play dividends for Trump, whose candidacy has divided Republican voters, elected officials, and party bigwigs.

“Attacking Obama and Hillary is a great way to unite Republicans,” said Mackowiak. “When you have as big a megaphone as Trump has, he can help unite Republicans every single day.”

Obama, of course, is poised to fight back.

He’s publicly knocked Trump on several occasions and he’s prepared to hit the campaign trail once primary season is officially over.

He’ll have a prime opportunity to skewer Trump at Saturday night’s White House Correspondents’ Association dinner. The dinner has given Obama practice: in 2011, he roasted Trump in his speech as the business mogul sat in the audience.

“Now, I know that he's taken some flak lately but no one is prouder to put this birth certificate matter to rest than The Donald,” Obama said. “And that's because he can finally get back to focusing on the issues that matter, like, did we fake the moon landing? What really happened in Roswell? And where are Biggie and Tupac?”

That dinner has spawned a legend that Trump’s campaign is an effort to overcome the humiliation he suffered at Obama’s hands. But Trump has denied that, telling The Washington Post this week "it’s such a false narrative.”

Trump also attended last year’s dinner but is skipping Saturday night’s. He told The Hill earlier this month that he didn’t want to read stories in the media misconstruing whether he had a good time.

“I was asked by every single group of media available to mankind [to attend this year]. But I've decided not to go,” he said. “Do you know why? I would have a good time and the press would say I look like I wasn't having a good time.”

The 2011 dinner came the night before the U.S. raid on Osama bin Laden’s compound in Pakistan.

On Monday, an interview Obama gave to CNN commemorating the fifth anniversary of the raid will be aired, another opportunity for him to relieve one of the most consequential weekends of his presidency.

There are risks for Obama being drawn into a war of words with Trump. Obama remains highly unpopular with Republicans and his appearance in the race could help galvanize his opponents.

There are dangers for Trump, too, in going head to head with the president.

Trump’s speech was panned by some Republican foreign policy hawks for providing few details and offering up contradictory solutions about how to defeat Islamic extremist groups in the Middle East.

They believe Trump's ideas will wilt under scrutiny from his opponents in the race.

And while the candidate's bombastic style has so far helped him rocket to the top of the GOP field, strategists say Trump will need to make specific, cogent attacks against Obama and Clinton to succeed.

“Reading a speech off a TelePrompter is not the same as going off the cuff on the campaign trail,” said Mackowiak. “If it’s more childish name calling, it’s not going to make a difference.”