The coalition between the two conservative nominees will benefit the country's economy in a post-election era, if Raeisi manages to assume power through the election.
Mohammad Baqer Qalibaf, the mayor of Tehran and a former head of the police, quit today and urged his supporters to vote on Friday for an even more conservative figure, Ebrahim Raisi, until recently the attorney-general. A survey by the state-affiliated Iranian Students Polling Agency last week showed the potential implications: support for Rouhani was at 42 percent, with Raisi on 27 percent and Qalibaf at 25 percent.
Qalibaf's allies had argued that he had more recognition in the capital Tehran and among young voters, and offered a more coherent economic plan than some other conservative candidates. "Qalibaf speaks more to the Iranian Revolutionary Guards and security apparatus, Raisi more to the traditional conservative".
Raisi is a former prosecutor and current custodian of Astan Quds Razavi, the foundation managing the affairs of Imam Reza's shrine, which has an annual revenue of $210 billion.
The president is viewed as the "moderate" choice and many see the election as something of a referendum on the policies that led to a landmark deal with global powers that saw Tehran curb its nuclear program in exchange for some sanctions relief.
The same day that Mr Trump heads overseas, Iran is holding its first presidential election since the completion of the nuclear agreement.
A reformist dropping out ahead of the 2013 election helped Rouhani edge out a almost 51 percent majority to win.
For the 12th time since the establishment of the Islamic Republic of Iran in 1979, Iranians will go to the polls on May 19 to vote for the lesser of two evils. It was after these humiliating experiences that the regime resorted to "engineering" the elections in favour of its candidate, Mahmoud Ahmadinejad, in 2005 and 2009.
Mr Rouhani, first elected in a landslide win four years ago on a promise to reduce Iran's worldwide isolation, is trying to hold on to office by firing up reformist voters disillusioned by a stalled economy and the slow pace of social reform. In April 2015, however, Khamenei said that if the nuclear negotiations were positive, and the United States "puts aside its typical ambiguities ... we will be able to negotiate with them on other issues".
High voter turnout has generally favored moderate and reformist candidates in Iran.
The Iranian Interior Ministry on April 20 announced the final list of six candidates vetted by the Guardian Council to run for president.