UBS' Colin Langan is juicing up his bear case for Tesla.

Even though the stock has gotten re-energized over the past month, the firm's US autos analyst cut his price target by 20% on Friday to $160 a share and reiterated his sell rating.

"We remain very cautious particularly as you go to the second half of the year. Consensus has them earning a profit," he said on CNBC's "Trading Nation." "With weakening deliveries and this consistent margin pressure, we expect losses in the second half."

Langan made the call just a few days before the electric automaker is expected to release second quarter delivery numbers. He believes they'll come in-line with Wall Street estimates. His forecast calls for 87,000 deliveries.

"I do think that will appease bulls who are looking for a pick-up in demand," he said. "What people might be missing is that Q2 earnings, I think, will be very challenged because a lot of the delivery push here was done by price cuts."

It's the third time Langan has reduced his Tesla target this year. He came into 2019 with a $230 target. Now, he has the third lowest on Wall Street, according to FactSet.

"Right now, it's really a story of margins and potential losses," he added. "It's a growth stock that did not exhibit growth in the first quarter, and so they need to get that growth story going again."

Yet, investors seem to like Tesla stock lately. Shares have rallied 18% over the past four weeks.

Langan has an explanation for the price action.

"You've got to realize that July 1 you'll have another about $1900 phase down of the U.S. energy tax credit. So, you actually have some pull forward this month as people getting ahead of that," Langan said. "I think demand actually will probably drop off more than people are expecting."

Disclosure: UBS, its affiliates or subsidiaries beneficially owned 1% or more Tesla shares as of last month.