General Motors (NYSE:GM) said it sold 1,642 Chevrolet Bolt EVs in the U.S. in June. That's the highest monthly total yet for U.S. sales of the little electric crossover, which became the first mass-market electric vehicle with a range over 200 miles when it was launched in December.

Tesla's (NASDAQ:TSLA) Model 3 may get a lot more media attention than GM's not-so-sexy little electric crossover. And it's likely that the Model 3's sales will outpace the Bolt's before too long.

But so far, at least, the Model 3 hype hasn't stopped GM from attracting more and more buyers to its own highly creditable electric entry.

A 2017 Chevrolet Bolt EV in silver.

Sales of General Motors' Chevrolet Bolt EV increased again in June. Image source: General Motors.

Bolt sales have been rising since early this year

Here's a look at how the Bolt's U.S. sales have stacked up month by month since its launch in December. 

A bar chart showing that GM sold 579 Bolts in the US in December, 1162 in January, 952 in February, 978 in March, 1292 in April, 1566 in May, and 1642 in June.

Data source: General Motors' U.S. sales reports.

GM filled initial orders from its dealers in California and Oregon -- the first dealers certified to sell the electric Chevy -- in December and January. Sales dipped a bit in February, after that initial rush of orders, but they've risen every month since as GM has ramped up production and gradually rolled out the Bolt to more dealers around the country.

The three owners with their Bolts in front of a Chevrolet dealership.

The first three Bolt EV owners received their new vehicles at a Chevrolet dealer in Fremont, California, in December. Left to right: Bobby Edmonds, William "Bill" Mattos, and Steve Henry. Image source: General Motors.

The total sales numbers are still fairly small, of course (consider that GM sold over 50,000 Chevy Silverado pickups in the U.S. last month), but it's likely that they'll keep growing for at least another few months. And even if they never get to Silverado levels, at some point, we'll be able to judge whether the Bolt is a success for GM. 

Why U.S. sales of the Bolt should climb further over the next few months

I expect Bolt sales to ramp up further over the next few months, because a lot of U.S. Chevy dealers just became eligible to order them. GM had only opened Bolt sales to dealers in a handful of states before June. But that changed on June 1, when GM opened its ordering system to all U.S. Chevrolet dealers that have completed GM's electric-vehicle training program. 

Bolts ordered in June will likely arrive at dealers sometime in August, a GM official said last month. Not coincidentally, GM is expected to launch a national marketing campaign for the Bolt later in the summer, just as those Bolts are arriving at dealerships.

Translation: If all goes according to plan, we should see a big bump in Bolt sales in September or thereabouts. 

At what point do we declare the Bolt to be a success?

It's hard to say exactly how many Bolts GM will have to sell to declare it a "success." (In a way, it's already a success: It's a good product that delivers on GM's promises.) But we have an idea of how many GM expected to produce when the Bolt was developed.

Back in mid-2015, as GM's engineers were working on turning the Bolt show car into a production vehicle, Reuters reported that GM's annual production goal was between 25,000 and 30,000. That includes production of both the Bolt and its Opel twin, the Ampera-e, for markets around the world. 

30,000 vehicles a year is just 2,500 a month (on average), though I strongly suspect that GM could boost that number considerably if demand warranted. With over 1,600 sold in the U.S. last month, and a sales boost expected by the end of the summer, GM may find itself needing to make some production decisions before long. 

But to the question: GM may well consider the Bolt to be a success at around 2,500 global sales a month, at least for now. 

(Side note: GM hasn't yet released global sales totals for the Bolt, but a GM spokesperson confirmed to me that it will begin doing so before long.) 

But what about the Model 3?

Tesla never quite manages to deliver on its lofty sales and production goals. But even so, monthly production (and sales) of the Model 3 should surpass the Bolt's well before the end of 2017.

Will that mean the Bolt is a failure? Not at all: GM created the Bolt as a statement at a time when it wasn't clear that there would be a retail market for electric cars not made by Tesla. GM hedged its bet by making the Bolt an urban runabout, a vehicle especially well-suited for ride-hailing and car-sharing services. The Bolt was also designed to be the platform for GM's autonomous-vehicle and connected-car development efforts. 

Chevrolet Bolt EVs with self-driving hardware on an assembly line at GM's Orion Assembly Plant in Michigan.

GM recently built 130 Bolts with self-driving systems. The self-driving Bolts will rack up miles to help GM refine its system before launch. Image source: General Motors.

Those decisions ensured that there would be a market for the Bolt. But at the same time, they probably limited the little crossover's appeal. The Bolt isn't sleek and sexy like a Tesla, something that led many analysts to conclude that GM missed the mark -- until they looked deeper at GM's intentions for the Bolt. 

The Model 3, on the other hand, is a sleekly styled compact luxury sports sedan, an electric alternative to BMW's huge-selling 3-Series and its rivals. Its natural market is a lot bigger: If it doesn't handily outsell the Bolt, Tesla has a problem.

The upshot: Keep in mind that the Bolt is a beginning

GM CEO Mary Barra has hinted that GM has more electric vehicles under development. We may look back in a few years and conclude that the Bolt was GM's proof of concept, a low-risk way to begin building the knowledge, resources, and supplier base that the company will need to transition more of its portfolio to electric drivetrains. 

I think the Bolt will be a success if GM sells as many as it expected -- and if the Bolt leads to more (and better-selling) electric vehicles from the General. I think both are likely, but we'll find out over the next several months.

John Rosevear owns shares of General Motors. The Motley Fool owns shares of and recommends Tesla. The Motley Fool recommends BMW. The Motley Fool has a disclosure policy.