When asked for comment on the requests, the federal Centers for Medicare and Medicaid Services confirmed it had received the senators' letter and would respond.
A CMS spokeswoman said, "Consistent with our aim to have a seamless open enrollment experience for consumers this year, the [HealthCare.gov] website is performing well and consumers can easily access enrollment tools to compare plans and prices."
"The deadline for people to shop and pick a plan for the upcoming year is December 15," she said. "We continue to encourage people to make plan selections by that deadline so that their coverage can begin on January 1."
CMS noted that the Dec. 15 deadline was originally proposed by the Obama administration to take effect next year.
States that have later deadlines than HealthCare.gov states, along with Idaho and Vermont, are: California, Colorado, Connecticut, Maryland, Massachusetts, Minnesota, New York, Rhode Island and Washington, as well as the District of Columbia.
EHealth's Flanders said his company is seeing a marked drop-off in sales to younger adults for Obamacare plans.
"Our mix is shifting to older enrollees," he said.
Insurance plans prefer younger customers because they tend to use fewer health services while paying premiums that support benefits for older, sicker enrollees.
In another worrisome trend, eHealth has seen an unprecedented number of consumers going through the enrollment process only to drop out at the last page when they see how much they would have to pay in premiums.
"They can't believe the prices," Flanders said.
Many eHealth consumers earn too much to qualify for federal subsidies, or tax credits, that lower a customer's monthly premium. Most customers of government-run marketplaces qualify for such discounts.
EHealth's survey of its customers who receive a subsidy showed 36 percent are paying $100 or less per month for their Obamacare plans and 75 percent are paying $300 or less per month.
But among nonsubsidized customers, 36 percent are paying $1,000 or more per month for their coverage and 81 percent are paying $500 or more.
Flanders said higher premiums seen this year are spurring the exodus of younger customers.
However, Obamacare advocates have noted that this year more customers than ever are able to find a health plan that will cost them $0 per month personally after their subsidies are factored in.
The zero-dollar plans are more common, ironically, because of big price hikes for many individual health plans this year.
When prices of Obamacare plans rise, so do the value of the subsidies for qualified customers. In many cases, those subsidies will be worth more than the monthly premium price.