Congress’s repeated efforts to repeal President Barack Obama’s signature health law have rattled insurance markets. Actions by President Trump and his administration have added still more uncertainty. Now, Senate Republicans have attached a provision to their $1.5 trillion tax cut that would repeal the health law’s mandate that most Americans have health insurance or pay a penalty.

All of those actions — along with flaws in the law itself — are having real-world impact.

“We share their pain,” Michael M. Dudley, the president and chief executive of Optima Health, said of his Virginia customers now shopping for policies on the health law’s online exchange. “The rate increases are very high. We can’t minimize that because it’s a fact.”

The Dixon family, which includes two girls ages 1 and 3, has been paying $988 a month this year for insurance provided by Anthem Blue Cross and Blue Shield. But Anthem plans will not be available in Charlottesville next year. The company told customers that uncertainty in the insurance market “does not provide the clarity and confidence we need to offer affordable coverage to our members.”

The online federal marketplace, HealthCare.gov, recommended another plan for Mr. Dixon in 2018. The new plan, offered by Optima Health, has premiums of $3,158 a month — about $37,900 a year — and an annual deductible of $9,200.

Alternatively, Mr. Dixon could pick a lower-cost plan offered by Optima with premiums of about $2,500 a month, or $30,000 a year. But the deductible would be much higher. The Dixons would need to spend $14,400 a year for certain health care services before Optima would begin to pay.

The Stovalls are facing similar mathematics.

“Our premiums will triple to $3,000 a month, with a $12,000 deductible, and that is far, far out of reach for us,” Ms. Stovall said after researching the options for her family of four on HealthCare.gov. “We are not asking for free health insurance. All we want is a reasonable chance to buy it.”