Democratic Sen. Joe Manchin appears in campaign ad for West Virginia GOP congressman who is challenging a Trump-backed lawmaker

• Manchin appeared in an ad for GOP Rep. David McKinley, who's facing a primary challenge from Alex Mooney.
• In boosting his fellow West Virginian, Manchin touted McKinley's opposition to the Build Back Better Act.

Sen. Joe Manchin last week appeared in a campaign advert for GOP Rep. David McKinley of West Virginia, a veteran lawmaker locked in bitter primary fight with Trump-endorsed congressman Alex Mooney.

In the 30-second ad, the centrist West Virginia Democrat touts his opposition to President Joe Biden's now-shelved Build Back Better legislation — the proposed social-spending bill that was set to fund critical investments in childcare, clean energy, and higher education, among other areas — in rebutting attacks against McKinley from Mooney.

Manchin, who endorsed Republican Sen. Susan Collins' reelection bid in 2020 and has thrown his support behind GOP Sen. Lisa Murkowski's reelection challenge this fall, displayed a more aggressive posture in the campaign spot, going after Mooney for being "all about" himself.

"I've always said if I can't go home and explain it, I can't vote for it — and that's why I opposed Build Back Better," Manchin said. "For Alex Mooney and his out-of-state supporters to suggest that David McKinley supported Build Back Better is an outright lie. David McKinley has always opposed reckless spending because it doesn't make sense for West Virginia."

The senator continued: "Alex Mooney has proven he's all about Alex Mooney. But West Virginians know David McKinley is all about us."

When asked if the ad signaled a full endorsement of McKinley, Sam Runyon, a spokesperson for Manchin, told CNN that the "ad speaks for itself."

After posting the video, McKinley's campaign touted Manchin's support on the Republican fundraising platform WinRed.

"Joe Manchin knows that I've always fought wasteful spending and opposed liberal policies that don't work for West Virginians," the message read.

Mooney responded to the ad on Saturday by criticizing McKinley's inclusion of Manchin.

"Further proof David McKinley is a complete and total RINO. Democrat Joe Manchin is endorsing him," he tweeted.

That McKinley would lean in on spreading the Manchin ad reflects the nature of the senator's bipartisan appeal in a state that in the last 25 years has shifted from a Democratic redoubt to a Republican stronghold.

Manchin — a former West Virginia Secretary of State and governor — was reelected to a second full term in the Senate in 2018 despite Trump's support of his then-opponent, state Attorney General Patrick Morrisey.

McKinley has been criticized by former President Donald Trump and Mooney-allied Republicans for backing the $1.2 trillion bipartisan infrastructure package that Biden signed into law last November. In supporting the bipartisan bill, McKinley was one of only 13 House Republicans to support the legislation.

McKinley pointed to the billions in funding that would be appropriated for much-needed West Virginia infrastructure projects; Mooney voted against the bill and is using the issue to rally the party faithfuls against McKinley.

McKinley and Mooney are facing off in a GOP primary contest due to West Virginia losing a congressional district after the state experienced a steady population decline from 2010 through 2020 — with the number of House seats in the state declining from three to two.

Republican Rep. Carol Miller currently represents the third congressional district, anchored in the southern portion of the state.