Hanoi (CNN) US President Donald Trump and North Korean leader Kim Jong Un won't be able to replicate the historic nature of their first summit as they meet here in the Vietnamese capital on Wednesday.

But their second summit will serve as a real test of whether the two men are indeed converting the optimism of their first meeting into a credible diplomatic endeavor capable of bringing about the long-sought denuclearization of North Korea.

That remained in question as Trump arrived in Hanoi on Tuesday to meet with Kim for a summit that is kicking off amid high stakes and low expectations . After months of high-level diplomacy, US officials have made clear that they do not yet know if North Korea is prepared to give up its nuclear weapons.

Here's what to watch as the two leaders meet face-to-face:

A relationship on display: The optics

Trump has consistently emphasized the importance of the personal relationship he has forged with Kim throughout his diplomatic engagement with North Korea.

He has referred to their written correspondence as "love letters" and praised Kim as "smart" and "tough." And during their last summit, the two men played to the cameras with broad smiles, laughter and mutual pats on the back.

With another eight months of trust-building between the two countries and still more "love letters" exchanged, the personal chemistry between the two men is sure to take center stage once again -- and expert observers will be analyzing every piece of body language.

While the second summit likely won't be able to deliver the drama of the first, the optics-conscious US President seeks to frame his second meeting with Kim as yet another show of his deal-making abilities.

Before a day of meetings on Thursday, Trump and Kim will sit down for dinner on Wednesday night, putting their one-on-one relationship at the center of the diplomatic effort.

But just as with the first summit, the stagecraft framing the summit in historic terms will also serve to elevate Kim to a position of prominence on the world stage, setting him on level footing with the American President and reducing his isolation among other world leaders.

The deliverables

But beyond the red-carpet treatment and the cheery chemistry that will likely color their meeting, the most persistent question hanging over Trump's second summit with the North Korean leader is simply: What will they achieve?

In the lead-up to the summit, senior Trump administration officials have sought to temper expectations, making clear that a dramatic leap toward the goal of denuclearization is not in the offing. But the summit will nonetheless be a test of whether Trump and Kim can put some meat on the bones of the largely rhetorical accomplishments of their Singapore meeting.

US and North Korean officials have been hammering out the contents of a joint declaration for the two leaders to agree to in Hanoi, and the Singapore declaration will be used as a benchmark to evaluate the pace of progress. If the Singapore declaration laid out the broad goals and areas of negotiation, how much more detail will the two leaders agree to in Hanoi? What specific commitments will the two sides make toward achieving the goals they agreed to in Singapore?

US officials have been tight-lipped about the agreement that is coming together, but the second joint declaration could address: a mutually agreed definition of North Korean denuclearization, steps toward normalizing diplomatic relations, inspections at North Korean facilities, a freeze in North Korea's nuclear activities or formalizing the steps to achieve denuclearization and a reduction in US sanctions.

What's clear is that the US will be looking to establish a clear framework for North Korea to take steps toward denuclearization. They are mindful that so far North Korea has yet to take any concrete and verifiable steps in that direction.

Split-screen effect

Trump's arrival in Hanoi on Tuesday set the stage for the split-screen images that will define much of the Hanoi summit: At nearly the same time Trump touched down, his former attorney and fixer Michael Cohen was arriving on Capitol Hill to give private testimony to senators about the President.

That imagery will be that much more jarring on Wednesday as Cohen testifies publicly before the House Oversight Committee.

Trump has vociferously slammed his longtime former aide as a liar and denied the allegations leveled against him -- but how much will he be distracted by Cohen's testimony while in Vietnam?

Trump's personal lawyer Rudy Giuliani told CNN's Pamela Brown that Trump is focused on his summit with Kim.

"I don't think Michael Cohen is occupying even 10% of his attention right now," Giuliani said.

But back in Washington at least, White House officials will be watching Cohen's public testimony and taking notes in case he wants to be briefed on the testimony, though a senior White House official said it's possible Trump will watch the hearing, which will start shortly after he wraps up a dinner with Kim in Hanoi.

It won't be the first time the various investigations that have dogged Trump flared up while he is overseas. Days before he departed for his first presidential trip abroad in 2017, the Justice Department named Mueller as special counsel. A year later, as Trump was preparing to meet Russian President Vladimir Putin in Finland, the Justice Department announced it was indicting 12 Russian nationals on charges of hacking Democrats' emails. And in December, Cohen pleaded guilty to a charge from Mueller's office days before Trump attended a leaders' summit in Argentina.

It's all led Trump to complain about the swirl of investigations, arguing it undermines his diplomatic effectiveness abroad.

Trump surprises?

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While US and North Korean officials continued to hash out the contents of the joint declaration in the days before the summit, there's another reason why US officials have declined to preview likely areas of agreement. And that's Trump's penchant for catching his own aides off guard.

In keeping with his "I alone can fix it" mantra -- and his frequently dim view of the government's subject-matter experts -- Trump has been known to jettison the carefully laid plans of his own government in favor of following his own instincts. That much has been clear in Trump's handling of world affairs, from US policy toward NATO to his approach to Russia.

During the Singapore summit, Trump agreed on the spot to suspend joint US-South Korean exercises. Trump and US officials had not previously planned to put the war games on the table, but Trump's in the moment move caught the US military's top brass and regional allies off guard.

Now, Trump's advisers have fretted about what surprise concession the President might make this time.

Among the most persistent concerns is that Trump would agree to reduce the US troop presence in South Korea. Those fears were allayed when the US and South Korea reached a new cost-sharing agreement just weeks before the summit, but when asked whether Trump would put the issue on the table during his summit with Kim, senior administration officials have merely said it is not an issue they have discussed with their North Korean counterparts.

How will Trump sell it?

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For Trump, if one half of his mission on the world stage is the diplomacy and the dealmaking, then the other half is the branding and salesmanship that the former reality TV star has so frequently brought to the presidency.

After the first summit in Singapore, Trump leaned into the historic nature of the first meeting between a sitting US president and North Korean leader. In a news conference after the summit, Trump focused on his swing from bellicose orator to peace-loving dealmaker. While the joint declaration offered little that North Korea had not previously agreed to, the symbolism of the summit helped back up his case.

But Trump also oversold the significance of the moment and his achievement, taking to Twitter as he made his way back to Washington to declare that "there is no longer a Nuclear Threat from North Korea." It is a point that top Trump administration officials have had to walk back as recently as Sunday, when Secretary of State Mike Pompeo acknowledged that a threat still exists.

Regardless of the extent of the progress this week, Trump is poised to sell the summit to the public as proof of his dealmaking abilities and evidence that he is disproving his critics. After all, Trump has increasingly sought to cast the reduced tensions and ongoing diplomacy with North Korea as a victory in and of itself.