Republican voters like having plenty of options but could quickly sour on negative campaigns.

The Republican presidential primary is a jumbled mass of competitors with new ones joining the jostling for support seemingly every week. Meanwhile the Democrats have more a coronation than a contest with one figure ignoring the rabble en route to the nomination.
So why did a May 18 Pew Research Center poll find that 57 of Republicans have an excellent or good impression of their partys candidates while 54 of Democrats have an excellent or good impression of theirs?
Bigger fields and active contests sometimes generate greater support than smaller fields and quiescent competitions. That happened in 2007 when Pew found 64 of Democrats liked their partys candidates while only 50 of Republicans did.
Theres also the quality of the contenders. In 2012 the GOP field was large but not particularly impressive. This time the quality of Republicans is far betterperhaps the best since 1980. Even some who ran last time such as former Texas Gov. Rick Perry have raised their game.
It also helps that the candidates are actually running campaigns. In 2011 for example Newt Gingrich and Rick Santorum lacked national organizations. They survived with successive plane tickets to the next of the 25 debates.
Perhaps the biggest reason Republicans are more satisfied with their field than Democrats is the opposition partys natural tendency to be hungrier and more energized after an eight year absence from the White House.
Being satisfied does not mean Republicans are decided however. Wednesdays Real Clear Politics average shows 15 GOP candidates with more than 1 support. But nearly 14 of Republican voters surveyed picked none of the above or said they didnt know yet. Of those who support a candidate many do so only weakly.
Most of the candidates who have declared or had a powerful public moment have received a modest bump. But shortly afterward they returned (roughly) to the mean as voters turned to new entrants or newsmakers.
GOP leaders elected officials activists and donors tell me that they and many Republicans they know are reserving judgment. They want to see which candidates demonstrate that they have what it takes to win. It is too early to know that nowand because Republicans so badly want to take back the White House they will spend more time studying the field even though they like what they see so far.
However if this group of candidates conducts itself as the last group did in 2011 and 2012 Republican enthusiasm will decline dramatically. Republicans did not like then and will like even less now personal attacks by GOP hopefuls on other Republican contenders.
Candidates are of course expected to draw contrasts in ways that depict competitors unfavorably by stressing who they are and what they believe. Republicans find it perfectly acceptable to say I am the only candidate who . . ." or Its time for a new generation" or Governors make decisions while senators cast votes."
But they reject direct attacks like those made in 2012 by Messrs. Gingrich and Perry against Mitt Romneys record at Bain Capital. That is why these attacks often hurt the aggressor more than the target. The Gingrich-Perry assaults on Bain demonized Mr. Romney with independents and energized Democrats in ways that he never fully recovered from but they also badly damaged the former House speaker and the Texas governor with GOP voters.
Republicans can help make a repeat performance less likely by using the power they may not understand that they have but would be wise to employ. As candidates struggle for support early in the campaign they are especially sensitive to the concerns of the grass roots. Thus concerned Republicans should let every candidate and potential candidate know what is acceptableand unacceptablebehavior.
With an email or letter to the campaign or a call to the local leader or fundraiser Republican voters can make clear that they expect candidates to demonstrate a governing vision an agenda that springs from conviction not convenience an ability to unify Republicans and a willingness to take their case to every community in America. They can also let each campaign know what they wont tolerate including ad hominem and dishonest attacks on fellow Republicans. Contrasting themselves with other contenders is one thing; trashing them is another.
Ronald Reagans 11th commandmentThou shalt not speak ill of any fellow Republican"is a powerful injunction. But in politics commandments are not delivered on stone tablets. They are best sent from the grass roots.
A version of this article appeared June 11 2015 in the U.S. edition of The Wall Street Journal with the headline The Promise And Problem Of A Big GOP Field and online at WSJ.com.