Joel K. Goldstein, the Vincent C. Immel Professor of Law at St. Louis University, is the author of two books on the vice presidency, most recently "The White House Vice Presidency: The Path to Significance, Mondale to Biden" (2016). The views expressed in this commentary are his.

(CNN) The job of any vice president of the United States includes being a salesperson for the administration and a defender of the president. Vice President Mike Pence is certainly not the first to make the case for the chief executive he serves, but none of Pence's predecessors has championed their president so consistently and effusively -- especially outside campaign season -- as has the 48th vice president. Pence has compared Donald J. Trump to Ronald Reagan and Theodore Roosevelt, and the accolades only go north from there.

Pence's vice presidential hyperbole was on early display when the Trump administration celebrated passage of the tax bill. At a Cabinet meeting and an afternoon event with Trump and Republican legislators, Pence extolled the President at length, on camera, with flattery that would have embarrassed most givers and receivers of compliments, including presidents and vice presidents of the past.

Some in the press noted that Pence praised Trump every 12 seconds during a three-minute stretch of the Cabinet meeting. Pence's performance has prompted adjectives such as fawning, groveling, toadying, sycophantic and less polite pejoratives

Pence has been an active vice president, something his recent engagement on the tax legislation and trip to Afghanistan underscore, but his obsequious behavior toward his boss raises troubling questions. The greatest worry about the sycophantic aspect of Pence's behavior is what it suggests about the operation of the presidency and the vice presidency.

Once derided as superfluous, the vice presidency has become a more important part of the daily work of the modern presidency, beginning with the service of Walter Mondale under President Jimmy Carter. Carter made Mondale an involved, general adviser and high-level assistant to the president on a consistent basis, and this practice has continued since then.

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Pence's predecessors from both parties -- Republicans George H.W. Bush, Dan Quayle and Dick Cheney and Democrats Mondale, Al Gore and Joe Biden -- all performed work that mattered during their four- or eight-year tenures. They brought the position new resources and developed recurring roles, all of which strengthened the second office and created new expectations and possibilities for its occupants. Most importantly, their expansion of the vice presidency offered the president much needed advice and help.

Ultimately, any vice president's influence and activities depend on his or her relationship with the president. A close link will bring a vice president into the room and send him on attractive assignments. It might also position an ambitious vice president as the president's political heir after their joint service ends.

Accordingly, all vice presidents, and not just Pence, work to develop and preserve rapport with that special constituency of one. Yet unlike Pence thus far, most recent vice presidents have largely demonstrated their loyalty without seeming servile. Cheney supported and praised George W. Bush without surrendering his individuality. And Biden did not compromise his brand even while being supportive of Barack Obama.

Pence serves a different president. A Google search of Trump and "narcissism" generates many hits, and reportedly advisers cater to the President's desire for praise. Many high-ranking Trump appointees have quickly lost favor with the President, demises that are cautionary tales for Pence and others.

Pence's constitutional role, as first successor, introduces an inherently awkward dynamic, but one that is exacerbated by an independent counsel investigation and an unusual amount of discussion of impeachment and lack of presidential inability. Trump, of course, can't remove Pence until the next election -- but he can marginalize his vice president and make his future less promising.

Pence may think public flattery is the right path to Trump's good side, but it's a risky course, because it potentially undermines Pence's credibility to hitch his star to such an unpopular and controversial president. All vice presidents must grapple with being perceived as followers, not leaders -- a perception Cheney and Biden avoided with their strong personalities and their public actions. Pence's flattery perpetuates an image of servility when he plays the role as Trump's prime celebrant as he did in his Cabinet meeting double-header.

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In reimagining the vice presidency four decades ago, Mondale emphasized the vice president's role as a counselor because he concluded that presidents suffered when they did not hear multiple sources of critical advice. He thought the vice president could add value as an occasional naysayer.

Mondale and his successors have performed that role in different ways and to varying degrees. For instance, Biden interjected frequently on discussions of Afghanistan and on other topics to make sure the president he served would hear a full airing of views. Perhaps Pence will, too.

But it's hard to imagine that a president who expects his vice president to lay it on as Pence has would be receptive to such honest and critical contributions, and it's hard to imagine a vice president who seems comfortable with such subservience would be willing to do so.

This commentary has been updated from an earlier version to clarify time references.