The Affordable Care Act reached a crucial milestone Monday, when it was reported that nearly 7 million people had signed up for coverage through the new health care marketplaces on the last official day of registration, marking the biggest expansion in health coverage since the creation of Medicare a half-century ago.

The sign-ups on the exchanges are just part of the story. About 4.5 million Americans have been covered under expanded Medicaid guidelines in states that have agreed to accept federal funding; 3 million young adults have been able to stay on their parents’ plan through the age of 26, and about 9 million have bought health plans directly through insurance companies (and not the exchanges). That adds up to about 23 million people, including at least 9.5 million people who had no insurance before, according to a study published by the Los Angeles Times.

It’s too early to call the new law a success: The mandate that employers provide employee health insurance or pay a penalty won’t go into effect until next year, and it will take some time to see if adding all these people to the private insurance system will have a stabilizing impact on rates.

But it’s not too soon to say that the Republican predictions that the Affordable Care Act would fall far short of 7 million sign-ups by the deadline were way off. And it’s also not too soon to say the same of the predictions from as recently as last week that there would be a net loss in the insured population when the gains were balanced against the number of people who lost policies that did not meet the law’s standard. The Los Angeles Times estimates the number of people uninsured as a result of the Affordable Care Act to be 1 million – too high to celebrate, but not so high that it wipes out the significance of the new sign-ups.

The law is far from perfect, but it’s time for Republicans to stop trying to undermine it and work to make it better. Republicans in Congress have not helped anyone by voting more than 40 times to repeal the law, or by gleefully predicting its failure.

A good start would be for Republicans in states like Maine that have refused to expand their Medicaid programs to accept federal funds to do so. Other ideas, such as the reforms suggested by independent Maine Sen. Angus King and four Democratic colleagues, could also head off problems for employees and companies.

And payment-reform demonstrations, like the Accountable Care Organization model under way in Maine, should be expanded so they can have an effect on controlling costs.

There is still time to offer alternatives to some of the law’s provisions and improve it. But it’s too late to start over.