Julian Zelizer, a history and public affairs professor at Princeton University and a CNN political analyst, is the author of " The Fierce Urgency of Now: Lyndon Johnson, Congress, and the Battle for the Great Society ." He's co-host of the "Politics & Polls" podcast. The opinions expressed in this commentary are his own.

(CNN) When President Donald Trump enters the annual G20 Summit this week, he will begin an important dialogue about a series of pivotal issues ranging from financial regulation to trade and immigration.

The conversations, which the G20 has been conducting since 1999, will involve cabinet-room style talks with all the leaders in this powerful group as well as side discussions between particular leaders focusing on the challenges that their respective nations face and tensions that exist between them. Most eagerly anticipated are the potential interactions between Presidents Donald Trump and Vladimir Putin.

But Trump walks into this summit with the United States now in a much weaker position than when he started his presidency. The President, who prides himself on making America great again, brings with him a set of liabilities that will make it more difficult for him to persuade others at this crucial gathering in Hamburg , Germany, to listen to his recommendations or fear his threats -- despite all the economic and military power that the United States brings to the table.

Social media unease

Let's begin with the tweets. Putting aside the specific content of the recent blasts from the Oval smart phone, the President's ongoing Twitter storms make all leaders uneasy. The heads of government in most nations prefer a certain amount of predictability and decorum from other heads of state. To have one of the most powerful people in the room being someone who is willing to send out explosive and controversial statements through social media, including nasty personal attacks or an edited video of him physically assaulting the media, does not make others at the G20 feel very confident about how he will handle deliberations with them.

Everyone knows that it is possible the next tweetstorm will be about them or that some of the conversations that were not intended for a mass audience could become public, thanks to the potential indiscretion of the President himself. Given his willingness to stretch the truth or say things that are false, this creates less than ideal conditions for negotiation.

Flouting international agreements

But it doesn't just stop with Twitter. The President has continually hammered away at international agreements that involve most of the leaders at the summit. His decision to withdraw from the Paris Climate Accord was devastating since many of the key players in the room, including Germany, strongly support this commitment to slow global warning.

His announcement was seen as a prime example of the kind of conservative unilateralism that they fear is also sweeping their own continents. The President's decision to simply say no, then claim there would be a possibility for renegotiation, caused huge ripples.

Trump has done the same with his broadsides against free trade agreements, a principle that has been a central goal for many of the nation's meeting at the table.

Given that most of the participants are working to achieve frameworks of agreement on all of these issues, Trump stands out as something of a bull in the china shop, who they simply don't trust. "Whoever believes that you can solve problems through isolation and protectionism is making a grave error," said German Chancellor Angela Merkel , "The world has become less united ... the discord is obvious and it would be dishonest to paper over the conflict."

Failure to deliver at home

The failure of the Trump administration to deliver on any major legislation at home since his inauguration and his continuing low approval ratings (despite his strong support with the base) also make him weaker overseas.

Historically, foreign leaders pay close attention to the domestic standing of a president to gauge whether he can deliver credible commitments or follow through on tougher threats. One of the factors that put President Richard Nixon in a strong position to pursue détente, a series of steps that aimed to ease tensions between the US and the Soviets, as well as China, was that he had created a strong political coalition after the 1968 election and was seen moving legislation and foreign policies forward in his first years in office.

In the current situation, especially in the wake of the health care fiasco, there is more than enough reason for other leaders at the summit to doubt whether Trump has the ability to really mobilize support for any deal once he is back in the states.

Then there is the Russia investigation, which continues to hang like a cloud over this administration. The investigation has two effects overseas. Like the tweets, it simply adds to the sense of instability that plagues Trump's presidency. In the same way that many leaders are not very confident about what the President will be doing or saying in the next few days, they, like Republicans on Capitol Hill, watch nervously to see what the next bombshell will be in the investigation, if any.

What's more, the investigation directly impinges on Trump's ability to be as effective as possible in dealing with Russia, a pivotal nation state in a number of military and diplomatic fronts, from Ukraine to Syria. Every conversation that the President has about Russia is tainted in the minds of many officials, who wonder whether this has to do with the investigations.

Even if the President and his team had serious ambitions to achieve a kind of détente with Russia to break through some of the logjams that exist overseas right now, those efforts will be difficult and many legislators -- in both parties -- will be unwilling to give him or Putin the benefit of the doubt that more productive relations are possible.

Secretary of State Rex Tillerson offered a reminder that the State Department, the strength of which has historically been essential for presidents to succeed overseas, is under siege from the White House. According to CNN, Tillerson reportedly gave a tongue-lashing to a high-ranking White House official about the need to let his department remain independent in hiring personnel, and for shooting down proposed nominees after months when State has been severely understaffed. Without the State Department's expertise, which the President needs to prepare and engage in discussions like those taking place in Germany, the US starts the negotiations with its hands tied behind its back.

Impact of first months of Trump presidency

The costs of Trump's governing style have become clearer in recent weeks. Despite the ongoing refrain from some of the punditry that that base still loves him and so the situation is not as bad as it seems, Trump has already done a lot to damage the US, domestically and abroad.

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We have been fortunate that there has not yet been a major international crisis or major terrorist attack in the US, since there are serious concerns about whether Trump would be able to respond effectively.

Last week, Republicans witnessed how their health care plans were undercut rather than helped by Trump. This week, as he goes into the summit with less leverage than another president would probably have, citizens see some of the costs overseas that have resulted from his weaknesses and political failures.