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) Senate Majority Leader Mitch McConnell is facing a major test this week. Since revealing the details of the Republican health care plan, McConnell has watched as a number of important senators in his own party announced their concerns or opposition. Some, such as Wisconsin Sen. Ron Johnson, have urged him to postpone the vote based on the assumption that, at this moment, it would not pass the upper chamber where the majority only has a slim 52 seats.

Meanwhile, on Monday, the Congressional Budget Office announced that under the Senate bill there would be 22 million more uninsured Americans by 2026, making McConnell's efforts to pass the bill that much more difficult.

But McConnell's supporters believe he can make this happen. They see McConnell as a modern-day Lyndon Johnson, who has served as both Senate minority and majority leader, an old-school legislator who can twist arms and cut deals to bring his party together. They are confident that despite all the potential problems with this bill, McConnell must have enough tricks up his sleeve to defy conventional wisdom.

But the truth is it's nearly impossible to predict if McConnell will succeed. To many, he has defined his career as an obstructionist rather than as someone who creates new policies. The challenge he faces this week is fundamentally different than much of what he has confronted in his time as a party leader.

Most of McConnell's skills have come as a member of the congressional minority or as a majority leader facing a president from the other party. Under those conditions, McConnell could be brilliant and devastating. Shortly after President Obama's inauguration, Utah Republican Bob Bennett recalled McConnell telling a retreat of Republicans : "We have a new president with an approval rating in the 70% area. We do not take him on frontally. We find issues where we can win, and we begin to take him down, one issue at a time."

His track record as an agent of obstruction is legendary. Throughout the Obama presidency, McConnell proved to be extremely effective at blocking many key legislative initiatives, from immigration reform to climate change regulations to criminal justice reform, that sometimes even commanded bipartisan support. The senator proved he knew how to whip up a no vote and to stand firm against intense political pressure to act.

He demonstrated the same savvy with judicial and executive branch appointments. McConnell was more than willing to let seats remain empty. Never was his ability to hold the party together as clear as when Justice Antonin Scalia died during President Obama's term. The Senate majority leader refused to even hold hearings on the nomination of Merrick Garland, based on the spurious argument that the next president should have the right to decide on the appointment. The seat remained vacant until a Republican controlled the White House.

As an obstructionist, McConnell demonstrated he was able to ignore the scrutiny of the media no matter how hot it became. When pundits and policymakers took to the airwaves to lambast the Republicans for failing to govern or for creating a constitutional crisis, McConnell didn't flinch. The breaking news cycle didn't faze him. He plays, as he titled his memoir, the "Long Game" with an eye on the needs of his party. Between 2009 and 2017, he kept up the pressure on his colleagues in the Senate to stick to their guns, and it worked.

Now the situation is different. For the first time in his career as a party leader (other than the brief moment he was selected as Senate majority leader in 2006), the public will see just how well he can perform in making things happen rather than blocking progress.

But the skills are different on the other side of the line of scrimmage.

Part of the job of the majority leader in times of united government is to bring disparate parts of the party together around proposals to change the status quo. "Trumpcare" would do just that. This is legislation that will strip away the health care benefits for millions of Americans and create a period of great uncertainty for health care markets.

Some conservatives want Congress to do much more in dismantling government. To them, the government would still be spending too much money subsidizing markets and leaving too many regulations in place. Others in the GOP are not willing to make such grandiose changes, realizing the effects it will have on their electorate. In particular, they fear the effects of the rollback of Medicaid on their populations as well as the higher deductibles that people with more illnesses will face.

Can McConnell bring these sides together, and work with the intransigent Freedom Caucus in the House, around legislation that will change the status quo and where Republicans will likely be blamed for any negative outcome?

In the modern era, part of the job of the majority leader has also been to sell ideas to the public. This is where the job of the obstructionist is very different than the job of the policy creator. Unlike some recent Senate majority leaders, McConnell doesn't really like to be on television and he tends to avoid reporters whenever possible. In this case, that comes at a cost since the natural face of the party is not out there convincing Americans why this is a good idea. That task is left to others, and right now his fellow salesmen, as reflected in public opinion polls about the health care bills, are doing a poor job.

Until now, President Trump has not tested McConnell, since he has focused almost exclusively on executive actions and avoided the legislative front on large-scale issues.

It is worth noting that McConnell does not really have many legislative issues that he is known for, other than his fierce opposition in the 1990s to campaign finance reform. This week he is dealing with a major issue that would have his signature in the history books.

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Can McConnell deliver on this controversial legislation? Can he play the part of leaders like Senate Majority Leader Mike Mansfield, who delivered when Democrats controlled the White House and Congress in the mid-1960s? Or, is this problematic bill something that is just too hot for this legislative leader to deliver?

This is a question that will be answered as the week unfolds.