“It’s basic customer service, like you would have in any other industry,” one Democratic congressional staffer said of answering calls for lawmakers.

But for the interns and staffers in member offices, these expletive-laced rants often cut deeper because the callers aren’t complaining about products: they’re complaining about lawmakers, their bosses.

On the Hill — where “Have a wonderful day!” is the preferred substitute for “Good riddance!” when dealing with rude callers — the line separating what’s considered abusive language and what’s considered a threat is often unclear.

Most current or former staffers and interns interviewed for this story didn’t want to be identified because they weren’t authorized to talk on the record about office operations.

Last week, Arkansas Republican Sen. Tom Cotton’s office was criticized for sending a cease and desist letter to members of a liberal activist group, Ozark Indivisible, for incessant phone calls and abusive language.

One of his constituents, Stacey Lane of Fayetteville, told ArkansasOnline that she received the ultimatum after she dropped “an f-bomb or two” during phone conversations with Cotton staffers.

Another called one of Cotton’s 19-year-old interns a “c–t,” one of his aides alleged on Twitter.

While multiple House and Senate offices from both parties confirmed it is uncommon to send cease and desist letters to harassing callers — and even though Cotton’s office said it did not receive any direct threats — the episode highlights the reality that congressional offices must often defuse aggressive calls from constituents that sometimes escalate into threats.

When that line is crossed, staffers are instructed to gather as much information as they can about the caller to help the U.S. Capitol Police build a file. This requires a level head and some coaxing.

Most angry callers don’t immediately identify themselves, one Democratic congressional aide said. Instead, “they just kind of go into their tirade. We have their phone number because of caller ID, but if we can get their name, usually that’s a good amount of information that we can pass along to Capitol Police.”

The USCP Threat Assessment Section is responsible for “investigating cases involving alleged threats against Members, their families or officers of Congress,” department spokeswoman Eva Malecki said in a statement.

Capitol Police investigators “work closely” with federal, state and local law enforcement on these cases to gather and share information.

After investigating the threat, the USCP returns to the office with a file on the person or persons of interest and guidance on how to handle the case.

If lawmakers feel their lives are in danger, or those of their families or employees, it is up to their offices to request extra security, whether that be at a campaign event in their district or at a function in Washington.

The mail never stops

Even as social media platforms like Twitter and Facebook provide direct routes for Americans to connect with their representatives, traditional mail correspondence and office calls have remained a popular method of engaging in the political process.

In fact, multiple current and former aides from both parties and chambers said the amount of phone calls and emails their offices received in 2017 was the highest they’d ever logged.

One Democratic House office received roughly “four times as much mail” last year than in any given year previously, according to a source with knowledge of such figures.

A staffer said his colleagues from other Senate offices agreed traditional correspondence was “through the roof” in 2017.

Every piece of correspondence — called in or written — is seen by a congressional staff member or intern, or sometimes even the lawmaker. Offices aim to respond within two weeks. They log every call and voicemail into a database, though there is no rule mandating such a practice.

Ugly America on the line

Even when constituents are not making direct threats, it’s in these conversations with teenage and college-age interns that Ugly America rears its head.

“We had one caller call a while ago, and all of a sudden he starts talking about how South Africa was better before apartheid ended,” one Senate office staffer said. “We’re not supposed to agree or disagree. We just say, ‘Thanks for calling!’”

Immigration is another hot-button — and often misunderstood — item that gets callers’ verbal acid flowing.

One staffer for a Florida congressman recently fielded a call from a man complaining that her boss was “speaking up on behalf of Puerto Ricans but not speaking up for constituents.”

The staffer was confused, so she kept him on the line to lure out what was prompting this feeling and realized he was talking about Puerto Ricans who relocated into the district after last year’s hurricanes.

“If you relocate from one state or one territory to another, you become a constituent. It doesn’t matter if they come from New York or Connecticut or Alabama or Puerto Rico,” she said.

The caller was upset the staffer would even insinuate Puerto Ricans were American citizens, she said.

“We should deport all of them,” the man yelled into the phone. “You only care about illegals.”

“That’s when I realized, ‘OK, there’s nothing I can say, no facts that I can give him, no position from the congressman I can give him — he’s just venting,’” the staffer said.

Drunk dialing

The steady stream of constituent calls does provide an immense vault of material for dark humor.

Some conversations are … colorful.

One college drinking game involves emailing or calling your representative’s office to leave a message.

Cleaning out and logging calls from the office voicemail inbox one Monday morning, a former Hill intern recalled excitedly searching for a tipsy message his friend had left while playing the game the previous Friday night. The message, short and grainy, but to the point: “Vote yes on taxes!” followed by garbled laughter.

Other calls involve unusual requests.

One House office recently heard from a constituent who asked for funds to pay for his grandmother’s funeral.

“We sympathized and pointed him to the right resources,” an aide in the office said, “but shared that unfortunately our offices could not help financially.”

Another caller asked the same House office for $10,000 in startup money for his “newly discovered opioid addiction herbal remedy.”

By his calculations, the drug would end up costing just $10 for the general public once it was mass produced. Unfortunately, lawmakers cannot use taxpayer dollars as venture capital. 

“After listening to his proposal, we shared with him that congressional offices are not allowed to do this,” the aide said. “He was furious and cursed at our staffer.”

And every office has its usual suspects.

“There are about a dozen to two dozen callers, you can say their name, and everyone in the office sort of laughs,” one Democratic Senate office source said.

That Senate office keeps a list of routine callers who are known to be “more difficult.” Interns are instructed to immediately transfer calls from those numbers to the more seasoned staff assistants, full-time employees who function as administrative caulk around the office, handling any workplace minutiae more senior staffers just don’t have time to address.

No lawmaker or office is spared its daily verbal lashing.

“You only have to work on the Hill for about five minutes to come across some strange constituent correspondence,” said Casey Harper, a former communications director for Missouri GOP Rep. Vicky Hartzler. “Learning how to handle these in a respectful, productive way is part of the job, and it’s not always easy.”

Watch: At the Table with Rep. Peter Welch