Joe Biden delivered a sly broadside against Bernie Sanders after accepting support from an anti-trans comedian. (Alex Wong/Getty)

US Democratic presidential candidate Joe Biden attempted a sly jab at fellow contender Bernie Sanders by stressing the importance of trans rights.

This week, the Vermont senator faced backlash after touting an endorsement from comedian Joe Rogan, known for his rap sheet of anti-trans statements.

“Let’s be clear,” the former vice president said in a tweet Saturday, “transgender equality is the civil rights issue of our time.”

“There is no room for compromise when it comes to basic human rights.”

Let’s be clear: Transgender equality is the civil rights issue of our time. There is no room for compromise when it comes to basic human rights. — Joe Biden (Text Join to 30330) (@JoeBiden) January 25, 2020

LGBT+ activists uneasy about Joe Biden’s trans support.

Coming at a heated time of the Democratic primaries with just weeks until the Iowa caucuses, the tweet was an implicit broadside against Sanders from Biden, who is running his third presidential bid.

With Biden’s support stalling, polls suggest, the tweet was received by many users as an attempt to capitalise on Sanders’ slip.

As a result, some LGBT+ activists cast doubt on the sincerity of the statement, given Biden’s track record of not always being in support of the community.

joe biden has exactly zero plan to do anything for trans people in terms of health care and basic legal protections. https://t.co/DRLqf8CE32 — ghost wife (@eponawest) January 25, 2020

fuck each and every one of the cis opportunists who pretend to care about us for the thirty seconds we’re useful as an attack on a political enemy https://t.co/pdKYEDuIq2 — Cara (@caraesten) January 26, 2020

Coming from the dude who's Civil Rights achievements are working with segregationists and writing the 1994 Crime Bill https://t.co/JNvRWUZrZQ — Logan Williams (@LoganWilliamsYo) January 25, 2020

Let’s reject the idea that only one issue is the civil rights issue of our time. It’s such a reductive, performative notion & does more harm to liberation movements than help. Stop putting forth these arguments that deepen the illusion of scarcity of our energy & resources. https://t.co/pi1zP0opwl — Raquel Willis (@RaquelWillis_) January 25, 2020

Joe Biden’s position in the Iowa polls is slipping.

Biden’s voting record has haunted him during the 2020 campaign. In his decades-long career as vice president and Delaware senator, Biden’s views on LGBT+ areas have changed.

Back in 1996, Biden voted in favor of the Defence of Marriage Act which defined marriage as between a male and female. Ten years later, he voted against the Federal Marriage Amendment.

But tides have changed since for the lawmaker, who came out in support of marriage equality before then president Barack Obama did.

Contenders are hitting the campaign trail in attempts to seize a sturdy lead in the volatile Iowa race. Sanders has secured 25 per cent of the vote, according to a New York Times poll, with Biden trailing a distant third behind Pete Buttigieg.

With Biden’s support stagnating, other runners are attempting to net the undecided voters, leading to bumps in the polls among Buttigieg’s base.

Voters are wrestling with who to side with and, after a year of campaigning, who prevails in Iowa may make or break which candidate ultimate battles Republican president Donald Trump.