Senate Minority Leader Mitch McConnell (R-Ky.) is urging his fellow Republicans to buck up Sen. Kyrsten Sinema of Arizona — a Democrat, sources familiar with the conversations tell Axios.

Why it matters: Republicans view Sinema and her moderate Democratic colleague Sen. Joe Manchin of West Virginia as their last line of defense against sweeping progressive laws — ranging from a $3.5 trillion social welfare bill to potentially irreversible structural changes like eliminating the filibuster and adding new states to the union.

Between the lines: Sen. Thom Tillis (R-N.C.) published an uncommon opinion piece Wednesday on the NBC News website thanking and crediting Sinema.

He praised the bipartisan infrastructure deal and said she’d taken more political risk than anyone, given that many progressives are now campaigning against her because she’s working with Republicans.