Phil Coulson been their handler for ten years and fifteen days when he has to make that call.
He was there on the day that they both came in, joined S.H.I.E.L.D however unwillingly. He remembers the day that he handed Barton a file when he was twenty-one years old and told him there was more to him than the past he was so desperately trying to escape. He still thinks that the need to avoid is the only reason that Barton joined the agency, and it's certainly what kept him there - at first, anyway - but the point is that it was his first real assessment as a potential handler and he had passed it by only taking an hour between giving Barton the opportunity and then finding the archer waiting in his motel room asking when he was to start work.
Six months later, Barton's first assessment in the field is presented, and Coulson's not entirely pleased when Fury informs him that he's going to be neutralising the infamous Black Widow. He knows little of her himself, other than that she has made quite a career as a self-employed assassin forhire, and that she's not fussy about who she works for. He's certainly a lot less happy when Barton goes in alone, but it's his chance to prove himself and as much as Coulson sees the potential in their newest recruit he's still just a number, just a rookie to Fury at this point, and he's replaceable if he becomes the Black Widow's next victim.
Coulson's a lot less happy when, after three days of radio silence from Barton, the young adult turns up in the pouring rain with a disgruntled teenager, proudly announcing that he'd found a new method of neutralising. The way that the Black Widow's lips are still swollen and their hair isn't all that damp, Coulson knows that they were responsible for the irritatingly loud relations from three rooms over.
Black Widow is seventeen years old when she becomes Agent Natasha Romanoff. She Americanises the name instantly, and he's quietly surprised about how easily she sheds the skin she adapted for herself in mother Russia. There's a bond with Barton that's formed during those three days of radio silence that can never be matched or understood. True, he feels responsible for them both and not just because Fury instructed him to, but at the end of the day, he bought Barton in and Barton bought Romanoff in, and for the first year of them working together he doesn't think twice about which one he'd bring out of the field alive if it came to a choice like that.
In that first year, Barton and Romanoff take jobs willingly. They're eager for the field, and it only takes him three hours of putting them in front of their assigned desks at H.Q. for him to hate the idea of giving them paperwork to complete because all it does is give him more to do himself. If he gives Barton a workout rota to complete, he's then forced to fill in mandatory health check requests because really, who can spent fifteen hours in the gym on a Monday? If he gives Romanoff surveillance footage to analyse she'll spot six other threats in the frame that Ops didn't pick up on and then its six new case files that need opening.
In their second year, Romanoff turns eighteen and celebrates by getting drunk and crawling into bed with Barton. Again. It's clear from the tension between them that even Coulson notices at times that it hasn't happened since that first night that Barton bought them in, but on the night of her eighteenth birthday (which he only knows from skimming through an older file) she finds two bottles of vodka, finishes them both to herself, and is then pounding on the door to Barton's quarters until he opens the door and she launches herself into his room.
The hallway is filled with sound for the entire night, and the shared vent system that makes up most of the airway makes Coulson actually put down his paperwork and escape to a place where he can't hear it because honestly, moments like this make him feel more like a father and less like a handler.
In the third year, Barton goes through what they later refer to as 'a phase'. He's twenty-three years old. He's found a girlfriend. And that's not Romanoff. Bonnie is a girl from another life, a life that it turns out he craves, and after three years of desperately escaping his past Bonnie is offering him a future that has potential for more than scars and an early grave. He sneaks out like the teenage boy he never was, he almost compromises an entire mission in Detroit to go and see her, and Coulson's debrief somewhat turns into a fatherly 'what the hell do you think you're playing at?' because yes, he's angry, and yes, he nearly ruined the mission, but mostly because Barton's disappearance left Romanoff without backup.
The fact that Romanoff is the one who brings Barton alcohol in the dead of night when he proposes to Bonnie and she disappears means that Romanoff will always have more patience for Barton's actions that Coulson ever could.
In the fourth year, they become childish with each other. Comfortable, but somewhat concerning. They're twenty and twenty-four years old, but they start squabbling over the coffee and yes, they are actually passing notes in debriefing. Coulson finds himself confiscating them, chosing to ignore the vague flashes of Russian that they scrawl in to each other, most of the time hoping that he was reading them wrong. He doesn't call them on their behaviour unless it poses a threat to a job though, because Barton's slowly bringing out a part of Romanoff that never existed.
The new nickname of 'Tash' brings out the Natasha to the Natasha Romanoff, and after that day she never signs her Russian name of Natalia again.
In the fifth year, it turns serious. Barton and Romanoff become two of the most respected agents in the field, and he's not quite sure what happened but he sends them to Budapest and no one is sure how they both make it out of that bloodbath alive. Coulson arrives at the rendevouz point and expects to find it empty, but instead finds them sat on a log at the side of a deserted road, leaning against each others shoulders as they hold themselves up on each other - it's mainly because Barton's leg is bleeding and his ankle looks broken, and he can see after a quick look at Romanoff that her shoulder is dislocated but his arm is still slung around her like she supposed him on his bad leg - but it's the truest display of partnership they've shown to date.
It's also the first time he realises that S.H.I.E.L.D operates on a policy that you save the mission first, your partner second, and that Barton and Romanoff disregard this rule above all others.
The sixth, seventh and eighth years progress is constant. They don't break any of their own records in the field because they've already peaked and they're holding that track record steady. They can't improve any more than their best, but they work at to their utmost to keep it a constant. During this years they start being sent on seperate missions, and he tries to handle them both seperately but it's hard when they find the strangest ways of contacting each other on a mission. When Barton is on a three-week stakeout with Sitwell in Algeria, Romanoff uses the cafe opposite their location to conduct her undercover operation in the same country.
Coulson watches the surveillance footage back from the operation and tries not to count the amount of times in an hour that Barton's head camera turns slightly to the right where she would fall into his line of sight, dressed as a waitress, but really, Barton, forty eight times?
Years nine and ten are hard. He will admit that. The Avengers Initiative is starting to come into play, and by now he has a strange emotion towards Barton and Romanoff that he likens to the way that Karen in Ops talks about her teenage children. In a strange way, he's more of a father than a handler, because Sitwell is a handler as well and he certainly doesn't have to deal with note-passing, secret messages, and past underage drinking. There's still drinking that causes problems, especially on Barton's thirtieth birthday when damnit, he actually has to bail them out of a Mexican prison. Really.
He sees the changes in administration, the plans that Fury has, and he does worry about how that might affect his time, especially when Romanoff goes in to Stark and he then joins Barton in New Mexico.
The worst part of that job is not the robot that tries to kill them, it's that for the first time he's aware of the deeper relationship forming between the two agents, because he sees the change in how Barton operates outside of a mission when Romanoff isn't there. During the clean up of missions, they guide each other, compensating for injured limbs by offering the other, because by some miracle they never end up with matching wounds though over the years their scars must match by now, but he deals with a brooding Barton in the car who hides a pout into a coffee that would have gone cold an hour before and tries not to say the words 'Romanoff will be fine' because he doesn't want to call Barton out on it.
And then it happens. Barton remains in New Mexico, and Romanoff goes back to Russia. And then Loki arrives in the New Mexico facility and it happens.
He's made calls to Romanoff plenty of times after a mission and it's never for calls that are good news. He's called her to tell her of other agent's deaths, of Barton's injuries in the field, and the call always starts with "Agent Romanoff..." because to him, that's who she is. It has always been her highest recognition of his respect that he calls her by the Americanised name she adopted herself when she became an agent of S.H.I.E.L.D.
Not this time, though. This is more personal. To her. To him.
"Natasha. Barton's been compromised..."