WASHINGTON (AP) — Senate Democrats’ campaign arm again outraised its Republican rival last month and borrowed $5.2 million to buy a Capitol Hill home next to its headquarters, according to campaign finance reports filed Friday.

Both campaign groups’ fundraising summaries showed donors were continuing to open wallets. Democrats are defending a narrow majority, and strategists from both parties say Republicans have a shot at picking up the six seats they need to claim that status for the first time since 2006’s elections.

Democratic donors gave $8.3 million to the Democratic Senatorial Campaign Committee in May. At the same time, officials said the committee saved $28.2 million.

GOP donors, meanwhile, gave the National Republican Senatorial Committee $5.8 million in May. The committee has saved $22.1 million.

Both committees are amassing sizeable bank accounts to pay for on-the-ground operatives and on-the-air television ads in tight races.

Democrats have outraised Republicans in 15 of the last 17 months.

Copyright 2014 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.