The first year of every presidency offers the best chance for legislative achievement, with the new chief executive, his party and their agenda at peak political strength.

That history raises questions about how much President Donald Trump will ever be able to get done with Congress. He approaches his first big test this week from a position of unusual weakness.

His top priority — replacing Obamacare with the American Health Care Act — has drawn opposition from both moderates and conservatives within his party. Trump has displayed little interest in the policy itself, casting it as a thankless chore to be done before getting to tax-cut legislation he values more.

As he seeks to pressure rebellious Republicans to abandon their opposition, Trump has the lowest standing in public opinion of any new president in modern history; 43 percent of Americans approve of his job performance, and 51 percent disapprove. according to the current realclearpolitics.com average. FBI Director James Comey told Congress this week he is investigating the possibility that Trump's campaign colluded with Russians who interfered with the 2016 campaign to help elect him.

Republicans hold 237 seats in the House and need 215 of them to support the new health-care bill on Thursday if the floor vote takes place as scheduled. With Trump and GOP leaders alike casting a victory as vital to the party's well-being, it's possible they can muster the party discipline to pass it.

Yet, the House Freedom Caucus maintains that 25 of its members are firmly committed to opposing it. Leading outside pressure groups, such as the Club for Growth and Heritage Action, are also urging "no" votes. It is also possible that GOP leaders will end up pulling the bill from the floor rather than face the possibility of defeat.

Defeat would amplify existing doubts about Trump's subsequent priorities. Republican leaders in Congress have all but declared the budget he unveiled this week to be dead on arrival.

On tax reform, House Speaker Paul Ryan is pushing a comprehensive tax overhaul plan that would cut the top personal rate to 33 percent and the top corporate rate to 20 percent, made possible by a new border adjustment tax that would hit imports while exempting exports. But numerous GOP senators strongly oppose the border adjustment tax, casting doubt on how much rates can be cut.