Sen. Bernie Sanders (I-Vt.) announced Thursday he will accompany patients with diabetes on a bus trip to Canada to buy insulin that's available at cheaper prices than in the U.S.

The move comes as Sanders seeks to burnish his progressive bona fides as he vows to lower drug costs if elected president.

He will make the trip with members of Insulin4All on July 28.

"Because of pharmaceutical industry greed, the U.S. price of insulin has nearly doubled in recent years, even though the drug can be purchased for one-tenth of the price in Canada," Sanders's campaign said in a statement. "That price discrepancy is widespread across many medicines, which has fueled the more than $69 billion in annual pharmaceutical industry profits, even while millions of Americans cannot afford the prescription drugs they need."

The campaign added that Sanders made a similar trip to Canada two decades ago, when he joined women with breast cancer on a trek to buy medication that was 10 percent of the price being charged in the Green Mountain State.

Sanders has sponsored legislation that would give the federal government the power to authorize generic versions of medicines if drug companies charge prices that are higher than those in other industrialized countries. He also introduced a bill in November to strip drug companies of their monopolies if their prices are deemed excessive.

Prescription drug prices have emerged as key issue for Democrats and the party's base. Several presidential candidates have released plans that they say would lower drug costs.

Sen. Elizabeth Warren (D-Mass.), one of Sanders's chief progressive rivals in the presidential primary field, has unveiled a plan that would allow the government to step in and manufacture certain drugs that lack competition.

Sens. Kamala Harris (D-Calif.) and Amy Klobuchar (D-Minn.), two other White House hopefuls, helped introduce a bill in December that would permit the government to intervene and stop certain price spikes for drugs.