Tim Kaine, left, and Mike Pence. (PBS NewsHour / YouTube)

Tuesday’s encounter between Tim Kaine and Mike Pence was substantive at times and contentious throughout. But the eminences who run the Commission on Presidential Debates should ask themselves this question: Why have a vice presidential debate at all?

Of course there should be some sort of public forum for voters to get to know the individuals who might find themselves, as the cliche goes, a heartbeat away from the presidency. But the debate format told us little about Kaine and Pence that we didn’t already know.

READ: Tim Kaine Puts Mike Pence on the Defensive as Candidates Take On Issues, and Each Other

For those keeping score on performance, I thought Pence was a bit more polished and poised. Kaine came out of the gate with the clear intention of being aggressive, and his tactic from the beginning was to interrupt the Indiana governor almost every time he spoke. By the midpoint of the debate, Pence, too was interrupting frequently when Kaine had the floor. But first impressions linger.

As for what the candidates said, it quickly became clear that the two men had little interest in talking to each other. Kaine was there to attack Republican candidate Donald Trump, and Pence was there to attack Democratic candidate Hillary Clinton. It is too soon to say who drew blood and how much, though I do think Kaine may have come away with more ammunition for attack ads.

Whenever the subject under discussion gave Kaine an opening — and quite often when it didn’t — Kaine reminded viewers of outrageous and offensive things Trump has said, such as his allegation that Mexican immigrants are “bringing drugs, they’re bringing crime, they’re rapists, and some, I assume, are good people.”

Pence actually tried to defend that statement, believe it or not. When Kaine raised other appalling Trump statements, Pence would generally shake his head in negation — which was odd, since all this stuff is on videotape — or pretend he hadn’t been listening.

Attempts by both candidates to land a knockout punch did not go well. During a discussion of Social Security — which Kaine claimed Trump and Pence want to privatize — Pence tried to echo Ronald Reagan: “There they go again,” he said, but it sounded contrived. Kaine, trying to capitalize on Trump’s problems of the last week, said that “Donald Trump can’t start a Twitter war with Miss Universe without shooting himself in the foot.” But the line totally missed the significance of Trump’s feud with Alicia Machado, which is that Trump’s behavior was sexist and cruel.

Moderator Elaine Quijano, armed with a long list of topics she wanted to cover, shifted gears briskly. She frequently cut off exchanges just when they were getting interesting. A bigger problem was that the candidates so often insisted on talking over each other. It was at times impossible to understand what either man was saying.

Pence did a lot of smiling, frowning and head-shaking while Kaine was speaking, and that’s generally not a good thing to do in a debate. Kaine kept his facial expressions under control, even his rogue eyebrow.

Kaine went after Trump for his temperament, his business bankruptcies, his refusal to release his income taxes, his boast that he is “smart” if he manages to avoid paying federal income taxes at all, his admiration of Russian President Vladimir Putin’s leadership qualities … so many issues, so little time. Trying to cram it all in made him sound rushed.

Pence’s list of particulars was shorter and his cadence slower, but he must have missed school the day his classmates learned what a non sequitur is. My favorite among many was when Quijano asked about the “intelligence surge” that Clinton proposes as part of her plan for fighting terrorism. Kaine went first and described the concept. Pence ignored the subject altogether and instead gave a prosecutorial soliloquy about Clinton’s emails.

For me, the most interesting part came at the end when Quijano asked about social issues. Kaine said his Catholic faith leads him to oppose both the death penalty and abortion — but that as governor of Virginia, he believed he was duty-bound to enforce laws allowing both. Pence spoke of being an evangelical Christian and explained why his faith leads him to oppose abortion. It sounded, finally, like a genuine discussion. But it lasted just a few minutes, and then the debate was over.

I know what Kaine and Pence got out of the evening: They established themselves as national political figures, and also managed to avoid harming their respective candidates’ chances. The benefit for voters, however, was harder to discern.

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