PEWAUKEE, Wis. — Appearing ever-more confident in Wisconsin’s primary, Republican presidential candidate Mitt Romney focused entirely on Democratic President Barack Obama during a campaign trip through this upper Midwestern battleground that could effectively seal the nomination for him Tuesday.

Fading rival Rick Santorum sought to stoke doubts about Romney’s conservative credentials on the last weekend of campaigning before the critical showdown. It’s Santorum’s last chance to prove his strength in the industrial heartland, where he said he can challenge Obama, but where Romney has beaten him consistently.

Still, Romney nodded toward evangelical conservatives Saturday, acknowledging the doubts in the former Massachusetts governor that linger with these voters, and foreshadowing the balancing act that will face him in the months to come.

“President Obama believes in a government-centered society. He believes government guiding our lives will do a better job in doing so than individuals,” Romney told more than 1,000 Wisconsin conservatives at a Faith and Freedom Coalition meeting in the heart of GOP-heavy Waukesha County.

With about half the GOP nominating contests complete, Romney has won 54 percent of the delegates at stake, putting him on track to reach the threshold 1,144 national convention delegates in June.

Santorum has won 27 percent of the delegates at stake. The former Pennsylvania senator, who has described Romney as too moderate on key issues to effectively confront Obama, would need to win 74 percent of the remaining delegates.

Still, cultural conservatives have struggled to embrace Romney. On average, in states where exit or entrance polls have been conducted, white evangelical conservatives have made up about half the GOP primary electorate.