Five things to watch as Clinton seeks to unite Democrats and Trump rattles Republicans yet again

With Hillary Clinton looking to unite the Democratic Party after her historic win in the U.S. primaries and Donald Trump rattling the Republican establishment once again, the coming week will be full of intrigue and possibilities.

The primaries may feel like history, but there is still much work to do for the Clinton and Trump campaigns: endorsements to seek, rivals to nudge out, party elites to mollify and new attack lines to test out. Here are five things to watch in the coming days.

1. Bernie goes to the White House

The senator from Vermont is no stranger to the White House and the President.

Bernie Sanders endorsed Barack Obama during his 2008 presidential bid and enthusiastically campaigned for his re-election four years ago. As U.S. senators, they voted against the Iraq war in 2003.

On Thursday, they will meet at the White House to talk about the campaign that Mr. Sanders ran in the primaries. The tone of the meeting will be congratulatory.

The two met in January in the days leading up to the start of the primaries – when a story circulating in the U.S. press quoted Mr. Obama as referring to Mr. Sanders as a "long shot" and a "bright, shiny object" whose lofty ideas deserved closer examination. Mr. Sanders has certainly exceeded everyone's expectations and built a loyal following.

The aim of the White House meeting will be to talk about how to bottle the success of the Sanders campaign and keep the millions of Democratic voters he has mobilized engaged in the general election campaign. Without the Democratic ticket winning the November presidential vote, Mr. Obama's legacy is in danger.

But the real question is whether Mr. Obama will try to persuade Mr. Sanders to suspend his campaign and unite behind Ms. Clinton.

2. The Obama endorsement

Mr. Obama has largely stayed on the sidelines during the Democratic primaries, allowing the candidates and voters space to debate the future of the party and who should be the standard-bearer in the election.

But there is little secret as to whom Mr. Obama favours. "She can govern and she can start here, Day One, more experienced than any non-vice-president has ever been who aspires to this office," he said of his former U.S. secretary of state during a Politico interview in January.

Now that the primaries are over, expect Mr. Obama to offer a full endorsement of Ms. Clinton.

The imagery will be powerful for the Democratic base and Democratic-leaning voters: an incumbent president with favourability ratings above 50 per cent rallying the party to get behind the presumptive nominee and block a Donald Trump presidency.

Mr. Obama's role in the election campaign will also be key. He likes to joke that his days of campaigning and asking for votes are long over. But the truth is, he is an effective and experienced campaigner. His appearances in support of the presumptive nominee could energize the campaign.

3. The Bern comes to an end

The Clinton campaign will be looking to bring Mr. Sanders into the fold quickly.

The worst-case scenario is a spurned Vermont senator badgering away at the presumptive nominee all the way to the convention in Philadelphia in July – and possibly beyond.

So far, Mr. Sanders has vowed to contest the District of Columbia primary next Tuesday (a footnote in the 2016 primaries) and continue the fight until the convention. He has virtually no chance of becoming the Democratic nominee, but there are other goals: a voice for the Sanders army in shaping the future of the party.

The party platform will need to be set at the convention, and Mr. Sanders will be looking to ensure that his strong stance on issues such as Wall Street regulation, free college tuition and criminal justice reform are endorsed by the party and become key messages in the election campaign.

Nudging him out of the race and getting him to endorse Ms. Clinton will require tact and diplomacy.

And then getting Mr. Sanders to persuade his supporters – who can be virulently anti-Clinton – to back the presumptive nominee and vote for Ms. Clinton in November will require the full skills of a political magician.

There are wounds to heal and fences to mend. But the same was true eight years ago when Ms. Clinton's White House aspirations were upended by a spirited Obama campaign and bad blood threatened the party.

The next days and weeks will show whether the Clinton and Sanders camps are striking the right notes at reconciliation and uniting the party for a blockbuster election.

4. Reining in the Donald

Mr. Trump has been on a tear in recent days, aiming his sharpest words at the federal judge presiding over the fraud case focusing on the failed Trump University venture. In a nutshell, he has argued that U.S. District Judge Gonzalo Curiel should not oversee the case because of his Mexican heritage.

His comments have rattled the Republican establishment – once again.

House of Representatives Speaker Paul Ryan called Mr. Trump's remarks the "textbook definition of a racist comment," but he said he would continue to back the Republican presumptive nominee. Senator Mark Kirk withdrew his support and said he would write in former Central Intelligence Agency director David Petraeus for president.

Mr. Trump has responded by dialling down the attacks. In his victory-night speech on Tuesday, it was a muted presumptive nominee reading off a Teleprompter – the kind of crutch he has ridiculed Ms. Clinton and other politicians for using.

But he cannot be chained to a Teleprompter. He has already announced that next week – probably Monday – he will deliver a speech about the Clintons.

Meanwhile, the Clinton campaign is not letting go of Trump University, pointing out that Mr. Trump's attacks on the federal judge are meant to distract from the truth of the case. Whereas previous attacks have focused on his temperament, arguing that he is unfit to be president, the Trump University case offers a different line of attack: Whether it's business or politics, Mr. Trump is in it for himself.

5. The coming ad wars

There will be an advertising onslaught – and much of it negative – over the next five months.

By the middle of May, Republican and Democratic groups had spent $408-million (U.S.) on TV ads during the primaries. All told, by the time voters go to the polls in November, a billion dollars will have been spent to flood the airwaves with hundreds of thousands of ads across the country, according to analysis by the Wesleyan Media Project.

The role of negative ads is to define a candidate early in the minds of voters. But that is going to be much harder this year because the candidates – Mr. Trump and Ms. Clinton – are pretty familiar to the electorate, explains Travis Ridout, a political science professor at Washington State University and co-director the Wesleyan Media Project .

"Still, I think it's going to be a very negative campaign. That's what Donald Trump does: He attacks other people. And Hillary Clinton's campaign is smart enough to know you can't let the attacks go unanswered," he said.

The period between the primaries and party conventions is not expected to see a huge amount of ad spending, but it is a time to try to define candidates and test lines of attack, according to Prof. Ridout.

This week, the Priorities USA Action Super PAC, which is backing Ms. Clinton, released a hard-hitting ad featuring a Ohio couple whose daughter was born with spina bifida. They share their reaction to Mr. Trump's appearing to mock a reporter with a disability earlier this year.

"When I saw Donald Trump mock somebody with a disability, it showed me his soul. It showed me his heart," Chris Glaros says in the ad, called Grace. "I didn't like what I saw."

The ad follows an even sharper ad released last month with voters mouthing disparaging comments made my Mr. Trump about women

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