PORTSMOUTH, N.H. — Hillary Rodham Clinton hit on a variety of subjects at her sun-splashed campaign rally here this weekend, but not once in her 30 minutes of speaking did she utter these words: Bernie Sanders.

Campaigning 1,200 miles away in Cedar Rapids, Iowa, Sanders was interrupted for applause 77 times – but not a single line in the senator’s nearly hour-long stump speech referred to Clinton or any other primary foe.

The Republican presidential campaign is being dictated by how the 17 candidates, led by Donald Trump, attack each other – from policy disagreements to nasty personal barbs.

The Democratic race stands in stark contrast. Despite tightening polls, the two leading candidates refuse to draw sharp contrasts, let alone criticize each other.

Ronald Reagan famously pronounced an 11th commandment: “Thou shalt not speak ill of any fellow Republican.” In 2016, however, it’s the Democrats who are heeding Reagan’s call – at least so far.

Sanders and his strategists have calculated that to beat Clinton he must expand the electorate – and that going negative will turn off voters.

“We have to follow the formula that brings people into the process,” said Sanders adviser Tad Devine.

Recent polls show Sanders gaining on or jumping ahead of Clinton – a surge he attributes to his progressive agenda to take on “the billionaire class.”

In New Hampshire, home to the nation’s first primary, a new NBC/Marist poll shows Sanders leading with 41 percent of Democratic voters, followed by Clinton at 32 percent. The same poll in July had Clinton ahead, 42 percent to 32 percent.

In Iowa, which holds the first caucuses, the NBC/Marist survey showed Clinton leading Sanders 38 percent to 27 percent. Her advantage there has narrowed since July, from 24 percentage points to 11.

Clinton assiduously has avoided referencing Sanders, in part because she cannot afford to alienate his impassioned supporters; should she win the party nomination, she will need their votes and enthusiasm in the general election.

To that end, Clinton has passed on even the easiest contrasts. She indisputably has more foreign policy experience than Sanders, yet gives her tenure as secretary of state nary a mention on the stump.

In a rare sit-down interview Friday, Clinton took what was widely interpreted as a veiled jab at Sanders. “You can wave your arms and give a speech, but at the end of the day are you connecting with and really hearing what people are either saying to you or wishing that you would say to them?” she told Andrea Mitchell of NBC News.

The next day, however, Clinton insisted, “I was talking about Donald Trump.”

Sen. Jeanne Shaheen, D-N.H., hit on the same theme Saturday. She said Clinton “always chooses to lift people up rather than tear people down.”

There is little doubt, however, that Clinton will try to tear Sanders down if and when she decides she needs to. Campaign surrogates have started doing her dirty work.

Sen. Claire McCaskill, D-Mo., said Sanders is too liberal. Connecticut Gov. Dan Malloy (D) said Sanders’s record on guns was “anathema” to Democrats. And Rep. Joaquin Castro, D-Texas, criticized his outreach to Latinos.

Asked about those volleys Saturday, Sanders said: “Don’t tell anybody: I think they’re getting nervous.”