Democrats have switched from defense to offense, going on the attack as insurers announce major increases in their premiums for Obamacare next year.

The party is blaming proposed hikes of up to 50 percent for some 2018 Obamacare plans on the Trump administration's efforts to create uncertainty in the individual market, which includes Obamacare's exchanges. However, some insurance plans have noted other factors in the proposed increases, including Obamacare's insurer tax.

Nevertheless, Democrats are highlighting the increases to show that Trump is seeking to torpedo the markets to promote his efforts to replace Obamacare.

"It is very clear that President Trump and Republicans here in Congress are not interested in improving the exchanges," said Sen. Chris Van Hollen, D-Md., during a press conference Thursday. "They are more focused on blowing them up."

Van Hollen pointed to some insurers citing uncertainty over the law's individual mandate requiring everyone to buy insurance and Trump's executive order that called for the government to relax enforcement of the mandate's penalties.

"Failure to enforce the individual mandate makes it far more likely that healthier, younger individuals will drop coverage and drive up the cost for everyone," said Chet Burrell, CEO of CareFirst, in Bloomberg News.

The insurer is seeking increases of as much as 50 percent for some plans in Maryland.

Van Hollen said that Burrell told him in a letter that a major part of the insurer's proposed increase is because of uncertainty over the individual mandate.

"He told me that if you only focus on medical inflation and the intensity of patient need in the pool, it would have been a 15 percent increase," he added.

Democrats were largely on defense last year when insurers requested an average 25 percent hike for the average Obamacare plan.

In the fall, for instance, Democrats responded that tax credits would rise to meet the increases.

"It's true that some premiums for midlevel health plans on the federal exchange could rise in the future, but it's also true that for most Americans on those plans, their ACA subsidies will rise to keep the plans affordable," former Democratic National Committee Chairwoman Donna Brazile said in October.

Now Democrats are employing more fiery rhetoric in talking about the increases. They are not making the same argument they made last year that tax credits would be increased to minimize any impact from the hikes.

Sen. Richard Blumenthal, D-Conn., said at the press conference Thursday that the administration is set on destabilizing the marketplaces to create leverage to pass the American Health Care Act.

"'Sabotage' is the operative word and political strategy for what they're doing," Blumenthal said.

The bill, which passed the House earlier this month, would partially repeal and replace Obamacare. But the Senate has sought to scrap that plan and is working on its own version.

The senators pointed to remarks that Trump made after the American Health Care Act was pulled from the House floor in March because of insufficient support. Trump said that the best thing to do politically was to just let Obamacare "explode."

In March, 44 Senate Democrats wrote to Trump and blasted the individual mandate executive order. The letter sent to Trump said that the president should "abandon" his efforts to repeal the law.

Other examples Democrats said were acts of sabotage include shortening the signup period for open enrollment from three months to 45 days for the 2018 coverage year.

They also pointed to the Trump administration not committing to paying insurance subsidies for lowering co-pays or deductibles for low-income Obamacare customers.

Trump has told the Washington Examiner that he wants to see what happens with the healthcare bill before committing to paying the subsidies next year, but insurers want an answer now since they are making plans for 2018.

Meanwhile, Republicans argue that the premium increases are further evidence that the law is collapsing.

The Republican National Committee sent out a press release on Thursday highlighting the big increases across the country.

"In 2017, many states announced double-digit increases in premium costs, making the 'Affordable Care Act' even more unaffordable," the RNC said. "Unless changes are made, these trends will continue in 2018 as Obamacare premiums are set to rise even further in several states."

A handful of states — Maryland, Virginia, Connecticut and Oregon — have publicly released proposed rates. The rates, which vary but mainly are in the double digits, could change after negotiations with state regulators.

Some states have seen insurers leave the market. For instance, Virginia saw Aetna leave the state's Obamacare's exchange due to mounting financial losses. Iowa's largest individual market insurer, Medica, recently told the Des Moines Register it could leave the market this year.

Not all insurers have pointed to market uncertainty or the potential loss of the individual mandate for the high prices. Some have pointed to lingering problems with the exchanges' risk pools and a looming tax on health insurers that goes into effect in 2018 after a one-year moratorium.

Sen. Chris Murphy, D-Conn., conceded there are some other factors for rate hikes.

"There is no doubt that a component of rate increases is going to be due to underlying healthcare costs," he said. "But this enormous percentage of rate increases due to the Trump administration is a self-inflicted wound."