NEW DELHI: US President Donald Trump has turned down the Indian government's invite to visit India on the occasion of Republic Day . This, TOI has learnt, was conveyed in the form of a letter to the Indian authorities recently.The letter is said to have comprised a regret message from Trump. The US president's domestic commitments, notably his State of the Union (SOTU) address, around that time of the year are apparently the reason for Trump not accepting India's invite.Trump's response is in sharp contrast to the one from his predecessor Barack Obama who, despite being faced with the same domestic presidential obligations in 2015, agreed to visit India as Republic Day chief guest.TOI had first reported on July 13 that India had officially invited Trump for Republic Day. While the US had confirmed the invite, it had said that the final decision would be taken after the inaugural 2+2 dialogue in September.Indo-US ties have been under strain lately because of differences over India's defence purchases from Russia and also its oil imports from Iran.Despite the US dangling the threat of CAATSA, the government went ahead and signed a deal to purchase S-400 air missile defence system with Russia during President Vladimir Putin's visit to India. In an interaction with some Indian journalists after Putin's visit, Russian ambassador Nikolay Kudashev complimented India for, as he said, following an independent foreign policy.India has also refused to stop, or even cut down drastically, oil imports from Iran. As US Secretary of State Mike Pompeo had said after the 2+2 dialogue here, US' "expectation" was that India, and indeed other countries, would bring down oil imports from Iran to zero by November 4 to avoid sanctions. India has said that it will be guided solely by its energy interests and its public sector companies are learnt to have already placed crude import orders with Iran for the month of November.The US formal response to India's invite brings to an end months of intense speculation about whether or not he would visit India for Republic Day celebrations. At one stage, in fact, India was so keen to host Trump that it offered to consider another set of dates for the visit in the month of February to avoid a clash with SOTU. However, the fact that NDA-2 is now into the final year of its five-year tenure also seems to have played on Trump's mind in turning down India's invite.Exactly why the Modi government chose to invite another US President, after Obama in 2015, for Republic Day remains open to speculation. Sources here said that the government had always chosen a Republic Day guest with the domestic audience in mind. The presence of a high-profile leader, it is felt, helps carry forward Modi's message, which the PM has often spoken about in his election speeches, about India's rising power and prestige in the global world.