can you summarize this Several studies (see Table 4) have assessed the impacts on the federal budget and have found them to be substantially different than the CBO anticipated. In particular, the costs of the exchange subsidies came in at well below CBO estimates initially (Spiro & Gruber, 2013), and total federal spending in 2018 on premium tax credits, cost-sharing reductions and risk adjustment was less than half of what CBO had projectedin large part because overall Marketplace enrollment was substantially lower than originally predicted (CBO, 2018; Elmendorf, 2012). More recently, however, actions by the Trump administration to weaken the law, including repeal of the individual mandate, may significantly worsen the risk pool in the exchanges (Aaron et al., 2017). Under the tax credit structure of the ACA, individuals pay a fixed percentage of their income for insurance, and the government pays the residual costs. As a result, these recent actions could significantly increase the federal budgetary costs of Marketplace subsidies, though if they reduce enrollment even more, the net effect compared to original estimates is unclear. The Medicaid expansion has been sizeable, with federal Medicaid spending in expansion states growing 12 percent faster than in non-expansion states (Sommers & Gruber, 2017). At the same time, overall Medicaid cost growth over the past decade has been much slower than predicted by actuaries at the Centers for Medicare and Medicaid Services (CMS)